diff --git a/mozilla/content/base/public/nsIDocument.h b/mozilla/content/base/public/nsIDocument.h
index 29b3d4f0a99..195491dd9f7 100644
--- a/mozilla/content/base/public/nsIDocument.h
+++ b/mozilla/content/base/public/nsIDocument.h
@@ -417,8 +417,8 @@ public:
   // Observation hooks for style data to propagate notifications
   // to document observers
   NS_IMETHOD StyleRuleChanged(nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint) = 0;
+                              nsIStyleRule* aOldStyleRule,
+                              nsIStyleRule* aNewStyleRule) = 0;
   NS_IMETHOD StyleRuleAdded(nsIStyleSheet* aStyleSheet,
                             nsIStyleRule* aStyleRule) = 0;
   NS_IMETHOD StyleRuleRemoved(nsIStyleSheet* aStyleSheet,
diff --git a/mozilla/content/base/public/nsIDocumentObserver.h b/mozilla/content/base/public/nsIDocumentObserver.h
index 5f9e71a86ca..fcb29b9bd97 100644
--- a/mozilla/content/base/public/nsIDocumentObserver.h
+++ b/mozilla/content/base/public/nsIDocumentObserver.h
@@ -281,15 +281,26 @@ public:
    * the document. The notification is passed on to all of 
    * the document observers.
    *
+   * Since nsIStyleRule objects are immutable, there is a new object
+   * replacing the old one.  However, the use of this method (rather
+   * than StyleRuleAdded and StyleRuleRemoved) implies that the new rule
+   * matches the same elements and has the same priority (weight,
+   * origin, specificity) as the old one.  (However, if it is a CSS
+   * style rule, there may be a change in whether it has an important
+   * rule.)
+   *
    * @param aDocument The document being observed
    * @param aStyleSheet the StyleSheet that contians the rule
-   * @param aStyleRule the rule that was modified
-   * @param aHint some possible info about the nature of the change
+   * @param aOldStyleRule The rule being removed.  This rule may not be
+   *                      fully valid anymore -- however, it can still
+   *                      be used for pointer comparison and
+   *                      |QueryInterface|.
+   * @param aNewStyleRule The rule being added.
    */
   NS_IMETHOD StyleRuleChanged(nsIDocument *aDocument,
                               nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint) = 0;
+                              nsIStyleRule* aOldStyleRule,
+                              nsIStyleRule* aNewStyleRule) = 0;
 
   /**
    * A StyleRule has just been added to a style sheet.
@@ -378,8 +389,8 @@ public:
                                                 PRBool aApplicable);         \
     NS_IMETHOD StyleRuleChanged(nsIDocument* aDocument,                      \
                                 nsIStyleSheet* aStyleSheet,                  \
-                                nsIStyleRule* aStyleRule,                    \
-                                nsChangeHint aHint);                         \
+                                nsIStyleRule* aOldStyleRule,                 \
+                                nsIStyleRule* aNewStyleRule);                \
     NS_IMETHOD StyleRuleAdded(nsIDocument* aDocument,                        \
                               nsIStyleSheet* aStyleSheet,                    \
                               nsIStyleRule* aStyleRule);                     \
@@ -515,9 +526,9 @@ _class::StyleSheetApplicableStateChanged(nsIDocument* aDocument,          \
 }                                                                         \
 NS_IMETHODIMP                                                             \
 _class::StyleRuleChanged(nsIDocument* aDocument,                          \
-                                       nsIStyleSheet* aStyleSheet,        \
-                                       nsIStyleRule* aStyleRule,          \
-                                       nsChangeHint aHint)                \
+                         nsIStyleSheet* aStyleSheet,                      \
+                         nsIStyleRule* aOldStyleRule,                     \
+                         nsIStyleRule* aNewStyleRule)                     \
 {                                                                         \
   return NS_OK;                                                           \
 }                                                                         \
diff --git a/mozilla/content/base/public/nsIStyleRule.h b/mozilla/content/base/public/nsIStyleRule.h
index d10791c3e38..d67723f1241 100644
--- a/mozilla/content/base/public/nsIStyleRule.h
+++ b/mozilla/content/base/public/nsIStyleRule.h
@@ -51,13 +51,54 @@ struct nsRuleData;
 #define NS_ISTYLE_RULE_IID     \
 {0x40ae5c90, 0xad6a, 0x11d1, {0x80, 0x31, 0x00, 0x60, 0x08, 0x15, 0x9b, 0x5a}}
 
+/**
+ * An object implementing |nsIStyleRule| (henceforth, a rule) represents
+ * immutable stylistic information that either applies or does not apply
+ * to a given element.  It belongs to an object or group of objects that
+ * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
+ * sheet).
+ *
+ * A rule becomes relevant to the computation of style data when
+ * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
+ * points to the rule.  (A rule node, |nsRuleNode|, is a node in the
+ * rule tree, which is a lexicographic tree indexed by rules.  The path
+ * from the root of the rule tree to the |nsRuleNode| for a given
+ * |nsStyleContext| contains exactly the rules that match the element
+ * that the style context is for, in priority (weight, origin,
+ * specificity) order.)
+ *
+ * The computation of style data uses the rule tree, which calls
+ * |nsIStyleRule::MapRuleInfoInto| below.
+ *
+ * It is worth emphasizing that the data represented by a rule
+ * implementation are immutable.  When the data need to be changed, a
+ * new rule object must be created.  Failing to do this will lead to
+ * bugs in the handling of dynamic style changes, since the rule tree
+ * caches the results of |MapRuleInfoInto|.
+ *
+ * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
+ * to typically being owned by their sheet), which are in turn garbage
+ * collected (with the garbage collection roots being style contexts).
+ */
+
+
 class nsIStyleRule : public nsISupports {
 public:
   NS_DEFINE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
 
   NS_IMETHOD GetStyleSheet(nsIStyleSheet*& aSheet) const = 0;
 
-  // The new mapping function.
+  /**
+   * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
+   * data represented by the rule that:
+   *   + are relevant for |aRuleData->mSID| (the style struct ID)
+   *   + are not already filled into the data struct
+   * into the appropriate data struct in |aRuleData|.  It is important
+   * that only empty data are filled in, since the rule tree is walked
+   * from highest priority rule to least, so that the walk can stop if
+   * all needed data are found.  Thus overwriting non-empty data will
+   * break CSS cascading rules.
+   */
   NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData)=0;
 
 #ifdef DEBUG
diff --git a/mozilla/content/base/src/nsDocument.cpp b/mozilla/content/base/src/nsDocument.cpp
index a3f49784477..95bfea94b54 100644
--- a/mozilla/content/base/src/nsDocument.cpp
+++ b/mozilla/content/base/src/nsDocument.cpp
@@ -2170,7 +2170,8 @@ nsDocument::AttributeChanged(nsIContent* aChild, PRInt32 aNameSpaceID,
 
 NS_IMETHODIMP
 nsDocument::StyleRuleChanged(nsIStyleSheet* aStyleSheet,
-                             nsIStyleRule* aStyleRule, nsChangeHint aHint)
+                             nsIStyleRule* aOldStyleRule,
+                             nsIStyleRule* aNewStyleRule)
 {
   PRInt32 i;
 
@@ -2183,7 +2184,7 @@ nsDocument::StyleRuleChanged(nsIStyleSheet* aStyleSheet,
     // XXXbz We should _not_ be calling BeginUpdate from in here! The
     // caller of StyleRuleChanged should do that!
     observer->BeginUpdate(this);
-    observer->StyleRuleChanged(this, aStyleSheet, aStyleRule, aHint);
+    observer->StyleRuleChanged(this, aStyleSheet, aOldStyleRule, aNewStyleRule);
 
     // Make sure that the observer didn't remove itself during the
     // notification. If it did, update our index and count.
diff --git a/mozilla/content/base/src/nsDocument.h b/mozilla/content/base/src/nsDocument.h
index 0d151bac1fe..1326f2fe74b 100644
--- a/mozilla/content/base/src/nsDocument.h
+++ b/mozilla/content/base/src/nsDocument.h
@@ -195,8 +195,8 @@ public:
                                               PRBool aApplicable) { return NS_OK; }
   NS_IMETHOD StyleRuleChanged(nsIDocument *aDocument,
                               nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint) { return NS_OK; }
+                              nsIStyleRule* aOldStyleRule,
+                              nsIStyleRule* aNewStyleRule) { return NS_OK; }
   NS_IMETHOD StyleRuleAdded(nsIDocument *aDocument,
                             nsIStyleSheet* aStyleSheet,
                             nsIStyleRule* aStyleRule) { return NS_OK; }
@@ -477,8 +477,8 @@ public:
                             PRInt32 aIndexInContainer);
 
   NS_IMETHOD StyleRuleChanged(nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint); // See nsStyleConsts fot hint values
+                              nsIStyleRule* aOldStyleRule,
+                              nsIStyleRule* aNewStyleRule);
   NS_IMETHOD StyleRuleAdded(nsIStyleSheet* aStyleSheet,
                             nsIStyleRule* aStyleRule);
   NS_IMETHOD StyleRuleRemoved(nsIStyleSheet* aStyleSheet,
diff --git a/mozilla/content/base/src/nsRuleNode.cpp b/mozilla/content/base/src/nsRuleNode.cpp
index 1bb258619e1..f26df07f013 100644
--- a/mozilla/content/base/src/nsRuleNode.cpp
+++ b/mozilla/content/base/src/nsRuleNode.cpp
@@ -553,74 +553,31 @@ nsRuleNode::PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched)
   return NS_OK;
 }
 
-nsresult
-nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
-{
-  NS_ASSERTION(aRule, "you should be using ClearCachedDataInSubtree");
-
-  nsRuleNode* ruleDest = this;
-  while (ruleDest) {
-    if (ruleDest->mRule == aRule)
-      break;
-    ruleDest = ruleDest->mParent;
-  }
-
-  if (ruleDest) {
-    NS_ASSERTION(ruleDest->mParent, "node must not be root");
-
-    // The rule was contained along our branch.  We need to blow away
-    // all cached data along this path.  Note that, because of the definition
-    // of inline style, all nodes along this path must have exactly one child.  This
-    // is not a bushy subtree, and so we know that by clearing this path, we've
-    // invalidated everything that we need to.
-    // XXXldb What about !important :hover rules, and such?
-    nsRuleNode* curr = this;
-    while (curr) {
-      curr->mNoneBits &= ~NS_STYLE_INHERIT_MASK;
-      curr->mDependentBits &= ~NS_STYLE_INHERIT_MASK;
-      if (curr->mStyleData.mResetData || curr->mStyleData.mInheritedData)
-        curr->mStyleData.Destroy(0, mPresContext);
-
-      if (curr == ruleDest)
-        break;
-
-      curr = curr->mParent;
-    }
-  }
-
-  return NS_OK;
-}
-
 PR_STATIC_CALLBACK(PLDHashOperator)
-ClearCachedDataInSubtreeHelper(PLDHashTable *table, PLDHashEntryHdr *hdr,
+ClearStyleDataHelper(PLDHashTable *table, PLDHashEntryHdr *hdr,
                                PRUint32 number, void *arg)
 {
   ChildrenHashEntry *entry = NS_STATIC_CAST(ChildrenHashEntry*, hdr);
-  nsIStyleRule* rule = NS_STATIC_CAST(nsIStyleRule*, arg);
-  entry->mRuleNode->ClearCachedDataInSubtree(rule);
+  entry->mRuleNode->ClearStyleData();
   return PL_DHASH_NEXT;
 }
 
 nsresult
-nsRuleNode::ClearCachedDataInSubtree(nsIStyleRule* aRule)
+nsRuleNode::ClearStyleData()
 {
-  if (aRule == nsnull || mRule == aRule) {
-    // We have a match.  Blow away all data stored at this node.
-    if (mStyleData.mResetData || mStyleData.mInheritedData)
-      mStyleData.Destroy(0, mPresContext);
+  // Blow away all data stored at this node.
+  if (mStyleData.mResetData || mStyleData.mInheritedData)
+    mStyleData.Destroy(0, mPresContext);
 
-    mNoneBits &= ~NS_STYLE_INHERIT_MASK;
-    mDependentBits &= ~NS_STYLE_INHERIT_MASK;
-
-    aRule = nsnull;  // Cause everything to be blown away in the descendants.
-  }
+  mNoneBits &= ~NS_STYLE_INHERIT_MASK;
+  mDependentBits &= ~NS_STYLE_INHERIT_MASK;
 
   if (ChildrenAreHashed())
     PL_DHashTableEnumerate(ChildrenHash(),
-                           ClearCachedDataInSubtreeHelper, aRule);
+                           ClearStyleDataHelper, nsnull);
   else
     for (nsRuleList* curr = ChildrenList(); curr; curr = curr->mNext)
-      curr->mRuleNode->ClearCachedDataInSubtree(aRule);
+      curr->mRuleNode->ClearStyleData();
 
   return NS_OK;
 }
@@ -649,11 +606,7 @@ nsRuleNode::PropagateNoneBit(PRUint32 aBit, nsRuleNode* aHighestNode)
 inline void
 nsRuleNode::PropagateDependentBit(PRUint32 aBit, nsRuleNode* aHighestNode)
 {
-  if (mDependentBits & aBit)
-    return; // Already set.
-
-  nsRuleNode* curr = this;
-  while (curr != aHighestNode) {
+  for (nsRuleNode* curr = this; curr != aHighestNode; curr = curr->mParent) {
     if (curr->mDependentBits & aBit) {
 #ifdef DEBUG
       while (curr != aHighestNode) {
@@ -665,7 +618,6 @@ nsRuleNode::PropagateDependentBit(PRUint32 aBit, nsRuleNode* aHighestNode)
     }
 
     curr->mDependentBits |= aBit;
-    curr = curr->mParent;
   }
 }
 
@@ -1148,223 +1100,223 @@ nsRuleNode::CheckSpecifiedProperties(const nsStyleStructID aSID,
 }
 
 const nsStyleStruct*
-nsRuleNode::GetDisplayData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetDisplayData(nsStyleContext* aContext)
 {
   nsRuleDataDisplay displayData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Display, mPresContext, aContext);
   ruleData.mDisplayData = &displayData;
 
-  return WalkRuleTree(eStyleStruct_Display, aContext, &ruleData, &displayData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Display, aContext, &ruleData, &displayData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetVisibilityData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetVisibilityData(nsStyleContext* aContext)
 {
   nsRuleDataDisplay displayData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Visibility, mPresContext, aContext);
   ruleData.mDisplayData = &displayData;
 
-  return WalkRuleTree(eStyleStruct_Visibility, aContext, &ruleData, &displayData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Visibility, aContext, &ruleData, &displayData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTextData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTextData(nsStyleContext* aContext)
 {
   nsRuleDataText textData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Text, mPresContext, aContext);
   ruleData.mTextData = &textData;
 
-  return WalkRuleTree(eStyleStruct_Text, aContext, &ruleData, &textData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Text, aContext, &ruleData, &textData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTextResetData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTextResetData(nsStyleContext* aContext)
 {
   nsRuleDataText textData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_TextReset, mPresContext, aContext);
   ruleData.mTextData = &textData;
 
-  return WalkRuleTree(eStyleStruct_TextReset, aContext, &ruleData, &textData, aComputeData);
+  return WalkRuleTree(eStyleStruct_TextReset, aContext, &ruleData, &textData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetUserInterfaceData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetUserInterfaceData(nsStyleContext* aContext)
 {
   nsRuleDataUserInterface uiData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_UserInterface, mPresContext, aContext);
   ruleData.mUserInterfaceData = &uiData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UserInterface, aContext, &ruleData, &uiData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UserInterface, aContext, &ruleData, &uiData);
   uiData.mCursor = nsnull;
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetUIResetData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetUIResetData(nsStyleContext* aContext)
 {
   nsRuleDataUserInterface uiData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_UIReset, mPresContext, aContext);
   ruleData.mUserInterfaceData = &uiData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UIReset, aContext, &ruleData, &uiData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UIReset, aContext, &ruleData, &uiData);
   uiData.mKeyEquivalent = nsnull;
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetFontData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetFontData(nsStyleContext* aContext)
 {
   nsRuleDataFont fontData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Font, mPresContext, aContext);
   ruleData.mFontData = &fontData;
 
-  return WalkRuleTree(eStyleStruct_Font, aContext, &ruleData, &fontData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Font, aContext, &ruleData, &fontData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetColorData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetColorData(nsStyleContext* aContext)
 {
   nsRuleDataColor colorData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Color, mPresContext, aContext);
   ruleData.mColorData = &colorData;
 
-  return WalkRuleTree(eStyleStruct_Color, aContext, &ruleData, &colorData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Color, aContext, &ruleData, &colorData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetBackgroundData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetBackgroundData(nsStyleContext* aContext)
 {
   nsRuleDataColor colorData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Background, mPresContext, aContext);
   ruleData.mColorData = &colorData;
 
-  return WalkRuleTree(eStyleStruct_Background, aContext, &ruleData, &colorData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Background, aContext, &ruleData, &colorData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetMarginData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetMarginData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Margin, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Margin, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Margin, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetBorderData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetBorderData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Border, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Border, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Border, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetPaddingData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetPaddingData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Padding, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Padding, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Padding, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetOutlineData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetOutlineData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Outline, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Outline, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Outline, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetListData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetListData(nsStyleContext* aContext)
 {
   nsRuleDataList listData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_List, mPresContext, aContext);
   ruleData.mListData = &listData;
 
-  return WalkRuleTree(eStyleStruct_List, aContext, &ruleData, &listData, aComputeData);
+  return WalkRuleTree(eStyleStruct_List, aContext, &ruleData, &listData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetPositionData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetPositionData(nsStyleContext* aContext)
 {
   nsRuleDataPosition posData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Position, mPresContext, aContext);
   ruleData.mPositionData = &posData;
 
-  return WalkRuleTree(eStyleStruct_Position, aContext, &ruleData, &posData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Position, aContext, &ruleData, &posData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTableData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTableData(nsStyleContext* aContext)
 {
   nsRuleDataTable tableData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Table, mPresContext, aContext);
   ruleData.mTableData = &tableData;
 
-  return WalkRuleTree(eStyleStruct_Table, aContext, &ruleData, &tableData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Table, aContext, &ruleData, &tableData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTableBorderData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTableBorderData(nsStyleContext* aContext)
 {
   nsRuleDataTable tableData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_TableBorder, mPresContext, aContext);
   ruleData.mTableData = &tableData;
 
-  return WalkRuleTree(eStyleStruct_TableBorder, aContext, &ruleData, &tableData, aComputeData);
+  return WalkRuleTree(eStyleStruct_TableBorder, aContext, &ruleData, &tableData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetContentData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetContentData(nsStyleContext* aContext)
 {
   nsRuleDataContent contentData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Content, mPresContext, aContext);
   ruleData.mContentData = &contentData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Content, aContext, &ruleData, &contentData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Content, aContext, &ruleData, &contentData);
   contentData.mCounterIncrement = contentData.mCounterReset = nsnull;
   contentData.mContent = nsnull; // We are sharing with some style rule.  It really owns the data.
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetQuotesData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetQuotesData(nsStyleContext* aContext)
 {
   nsRuleDataContent contentData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Quotes, mPresContext, aContext);
   ruleData.mContentData = &contentData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Quotes, aContext, &ruleData, &contentData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Quotes, aContext, &ruleData, &contentData);
   contentData.mQuotes = nsnull; // We are sharing with some style rule.  It really owns the data.
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetXULData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetXULData(nsStyleContext* aContext)
 {
   nsRuleDataXUL xulData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_XUL, mPresContext, aContext);
   ruleData.mXULData = &xulData;
 
-  return WalkRuleTree(eStyleStruct_XUL, aContext, &ruleData, &xulData, aComputeData);
+  return WalkRuleTree(eStyleStruct_XUL, aContext, &ruleData, &xulData);
 }
 
 #ifdef MOZ_SVG
 const nsStyleStruct*
-nsRuleNode::GetSVGData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetSVGData(nsStyleContext* aContext)
 {
   nsRuleDataSVG svgData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_SVG, mPresContext, aContext);
   ruleData.mSVGData = &svgData;
 
-  return WalkRuleTree(eStyleStruct_SVG, aContext, &ruleData, &svgData, aComputeData);
+  return WalkRuleTree(eStyleStruct_SVG, aContext, &ruleData, &svgData);
 }
 #endif
 
@@ -1372,8 +1324,7 @@ const nsStyleStruct*
 nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
                          nsStyleContext* aContext, 
                          nsRuleData* aRuleData,
-                         nsRuleDataStruct* aSpecificData,
-                         PRBool aComputeData)
+                         nsRuleDataStruct* aSpecificData)
 {
   // We start at the most specific rule in the tree.  
   nsStyleStruct* startStruct = nsnull;
@@ -1496,9 +1447,6 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
   }
 
   // We need to compute the data from the information that the rules specified.
-  if (!aComputeData)
-    return nsnull;
-  
   ComputeStyleDataFn fn = gComputeStyleDataFn[aSID];
   const nsStyleStruct* res = (this->*fn)(startStruct, *aSpecificData, aContext, highestNode, detail,
                                          !aRuleData->mCanStoreInRuleTree);
@@ -4491,14 +4439,17 @@ nsRuleNode::GetStyleData(nsStyleStructID aSID,
     NS_NOTREACHED("dependent bits set but no cached struct present");
   }
 
+  if (!aComputeData)
+    return nsnull;
+
   // Nothing is cached.  We'll have to delve further and examine our rules.
   GetStyleDataFn fn = gGetStyleDataFn[aSID];
   if (!fn) {
     NS_NOTREACHED("unknown style struct requested");
     return nsnull;
   }
-  data = (this->*fn)(aContext, aComputeData);
-  if (data || !aComputeData)
+  data = (this->*fn)(aContext);
+  if (data)
     return data;
 
   NS_NOTREACHED("could not create style struct");
diff --git a/mozilla/content/base/src/nsStyleContext.cpp b/mozilla/content/base/src/nsStyleContext.cpp
index 810984b4290..f6daeb03e54 100644
--- a/mozilla/content/base/src/nsStyleContext.cpp
+++ b/mozilla/content/base/src/nsStyleContext.cpp
@@ -396,27 +396,20 @@ nsStyleContext::ApplyStyleFixups(nsIPresContext* aPresContext)
 }
 
 void
-nsStyleContext::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule)
+nsStyleContext::ClearStyleData(nsIPresContext* aPresContext)
 {
-  PRBool matched = PR_TRUE;
-  if (aRule)
-    mRuleNode->PathContainsRule(aRule, &matched);
-  
-  if (matched) {
-    // First we need to clear out all of our style data.
-    if (mCachedStyleData.mResetData || mCachedStyleData.mInheritedData)
-      mCachedStyleData.Destroy(mBits, aPresContext);
+  // First we need to clear out all of our style data.
+  if (mCachedStyleData.mResetData || mCachedStyleData.mInheritedData)
+    mCachedStyleData.Destroy(mBits, aPresContext);
 
-    mBits = 0; // Clear all bits.
-    aRule = nsnull; // Force all structs to be blown away in the children.
-  }
+  mBits = 0; // Clear all bits.
 
   ApplyStyleFixups(aPresContext);
 
   if (mChild) {
     nsStyleContext* child = mChild;
     do {
-      child->ClearStyleData(aPresContext, aRule);
+      child->ClearStyleData(aPresContext);
       child = child->mNextSibling;
     } while (mChild != child);
   }
@@ -424,7 +417,7 @@ nsStyleContext::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule
   if (mEmptyChild) {
     nsStyleContext* child = mEmptyChild;
     do {
-      child->ClearStyleData(aPresContext, aRule);
+      child->ClearStyleData(aPresContext);
       child = child->mNextSibling;
     } while (mEmptyChild != child);
   }
diff --git a/mozilla/content/base/src/nsStyleSet.cpp b/mozilla/content/base/src/nsStyleSet.cpp
index be03afc5468..9baf2b190e9 100644
--- a/mozilla/content/base/src/nsStyleSet.cpp
+++ b/mozilla/content/base/src/nsStyleSet.cpp
@@ -195,7 +195,7 @@ public:
 
   virtual nsresult GetRuleTree(nsRuleNode** aResult);
   
-  virtual nsresult ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule);
+  virtual nsresult ClearStyleData(nsIPresContext* aPresContext);
 
   virtual nsresult GetStyleFrameConstruction(nsIStyleFrameConstruction** aResult) {
     *aResult = mFrameConstructor;
@@ -254,20 +254,6 @@ public:
                               PRInt32 aModType, 
                               nsChangeHint aHint); // See nsStyleConsts fot hint values
 
-  // xxx style rules enumeration
-
-  // Style change notifications
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint); // See nsStyleConsts fot hint values
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule);
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule);
-
   // Notification that we were unable to render a replaced element.
   NS_IMETHOD CantRenderReplacedElement(nsIPresContext* aPresContext,
                                        nsIFrame*       aFrame);
@@ -1504,30 +1490,13 @@ StyleSetImpl::GetDefaultStyleData()
 }
 
 nsresult
-StyleSetImpl::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule)
+StyleSetImpl::ClearStyleData(nsIPresContext* aPresContext)
 {
-  // XXXdwh This is not terribly fast, but fortunately this case is rare (and often a full tree
-  // invalidation anyway).  Improving performance here would involve a footprint
-  // increase.  Mappings from rule nodes to their associated style contexts as well as
-  // mappings from rules to their associated rule nodes would enable us to avoid the two
-  // tree walks that occur here.
-  
-  // Crawl the entire rule tree and blow away all data for rule nodes (and their descendants)
-  // that have the given rule.
   if (mRuleTree)
-    mRuleTree->ClearCachedDataInSubtree(aRule);
-  
-  // We need to crawl the entire style context tree, and for each style context we need 
-  // to see if the specified rule is matched.  If so, that context and all its descendant
-  // contexts must have their data wiped.
-  nsCOMPtr<nsIPresShell> shell;
-  aPresContext->GetShell(getter_AddRefs(shell));
-  nsIFrame* rootFrame;
-  shell->GetRootFrame(&rootFrame);
-  if (rootFrame) {
-    nsStyleContext* rootContext = rootFrame->GetStyleContext();
-    if (rootContext)
-      rootContext->ClearStyleData(aPresContext, aRule);
+    mRuleTree->ClearStyleData();
+
+  for (PRInt32 i = mRoots.Count() - 1; i >= 0; --i) {
+    NS_STATIC_CAST(nsStyleContext*,mRoots[i])->ClearStyleData(aPresContext);
   }
 
   return NS_OK;
@@ -1761,33 +1730,6 @@ StyleSetImpl::AttributeChanged(nsIPresContext* aPresContext,
                                              aNameSpaceID, aAttribute, aModType, aHint);
 }
 
-
-// Style change notifications
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleChanged(nsIPresContext* aPresContext,
-                               nsIStyleSheet* aStyleSheet,
-                               nsIStyleRule* aStyleRule,
-                               nsChangeHint aHint)
-{
-  return mFrameConstructor->StyleRuleChanged(aPresContext, aStyleSheet, aStyleRule, aHint);
-}
-
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleAdded(nsIPresContext* aPresContext,
-                             nsIStyleSheet* aStyleSheet,
-                             nsIStyleRule* aStyleRule)
-{
-  return mFrameConstructor->StyleRuleAdded(aPresContext, aStyleSheet, aStyleRule);
-}
-
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleRemoved(nsIPresContext* aPresContext,
-                               nsIStyleSheet* aStyleSheet,
-                               nsIStyleRule* aStyleRule)
-{
-  return mFrameConstructor->StyleRuleRemoved(aPresContext, aStyleSheet, aStyleRule);
-}
-
 NS_IMETHODIMP
 StyleSetImpl::CantRenderReplacedElement(nsIPresContext* aPresContext,
                                         nsIFrame*       aFrame)
diff --git a/mozilla/content/html/document/src/nsHTMLContentSink.cpp b/mozilla/content/html/document/src/nsHTMLContentSink.cpp
index ef3f235f818..2f292ab10ff 100644
--- a/mozilla/content/html/document/src/nsHTMLContentSink.cpp
+++ b/mozilla/content/html/document/src/nsHTMLContentSink.cpp
@@ -5448,7 +5448,8 @@ HTMLContentSink::StyleSheetApplicableStateChanged(nsIDocument *aDocument,
 NS_IMETHODIMP
 HTMLContentSink::StyleRuleChanged(nsIDocument *aDocument,
                                   nsIStyleSheet* aStyleSheet,
-                                  nsIStyleRule* aStyleRule, nsChangeHint aHint)
+                                  nsIStyleRule* aOldStyleRule,
+                                  nsIStyleRule* aNewStyleRule)
 {
   return NS_OK;
 }
diff --git a/mozilla/content/html/style/public/nsICSSStyleSheet.h b/mozilla/content/html/style/public/nsICSSStyleSheet.h
index 6ccaa54f77d..7c863be0dba 100644
--- a/mozilla/content/html/style/public/nsICSSStyleSheet.h
+++ b/mozilla/content/html/style/public/nsICSSStyleSheet.h
@@ -64,12 +64,14 @@ public:
 
   NS_IMETHOD  PrependStyleRule(nsICSSRule* aRule) = 0;
   NS_IMETHOD  AppendStyleRule(nsICSSRule* aRule) = 0;
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew) = 0;
 
   NS_IMETHOD  StyleRuleCount(PRInt32& aCount) const = 0;
   NS_IMETHOD  GetStyleRuleAt(PRInt32 aIndex, nsICSSRule*& aRule) const = 0;
 
   NS_IMETHOD  DeleteRuleFromGroup(nsICSSGroupRule* aGroup, PRUint32 aIndex) = 0;
   NS_IMETHOD  InsertRuleIntoGroup(const nsAString & aRule, nsICSSGroupRule* aGroup, PRUint32 aIndex, PRUint32* _retval) = 0;
+  NS_IMETHOD  ReplaceRuleInGroup(nsICSSGroupRule* aGroup, nsICSSRule* aOld, nsICSSRule* aNew) = 0;
 
   NS_IMETHOD  StyleSheetCount(PRInt32& aCount) const = 0;
   NS_IMETHOD  GetStyleSheetAt(PRInt32 aIndex, nsICSSStyleSheet*& aSheet) const = 0;
diff --git a/mozilla/content/html/style/src/nsCSSParser.cpp b/mozilla/content/html/style/src/nsCSSParser.cpp
index b248ffea8a2..e52cb771735 100644
--- a/mozilla/content/html/style/src/nsCSSParser.cpp
+++ b/mozilla/content/html/style/src/nsCSSParser.cpp
@@ -640,12 +640,11 @@ CSSParserImpl::ParseStyleAttribute(const nsAString& aAttributeValue,
   if (declaration) {
     // Create a style rule for the delcaration
     nsICSSStyleRule* rule = nsnull;
-    rv = NS_NewCSSStyleRule(&rule, nsnull);
+    rv = NS_NewCSSStyleRule(&rule, nsnull, declaration);
     if (NS_FAILED(rv)) {
       declaration->RuleAbort();
       return rv;
     }
-    rule->SetDeclaration(declaration);
     *aResult = rule;
   }
   else {
@@ -1473,14 +1472,13 @@ PRBool CSSParserImpl::ParseRuleSet(PRInt32& aErrorCode, RuleAppendFunc aAppendFu
   // Translate the selector list and declaration block into style data
 
   nsCOMPtr<nsICSSStyleRule> rule;
-  NS_NewCSSStyleRule(getter_AddRefs(rule), slist);
+  NS_NewCSSStyleRule(getter_AddRefs(rule), slist, declaration);
   if (!rule) {
     aErrorCode = NS_ERROR_OUT_OF_MEMORY;
     delete slist;
     return PR_FALSE;
   }
   rule->SetLineNumber(linenum);
-  rule->SetDeclaration(declaration);
   (*aAppendFunc)(rule, aData);
 
   return PR_TRUE;
diff --git a/mozilla/content/html/style/src/nsCSSRules.cpp b/mozilla/content/html/style/src/nsCSSRules.cpp
index aed43a7e994..a70066583fe 100644
--- a/mozilla/content/html/style/src/nsCSSRules.cpp
+++ b/mozilla/content/html/style/src/nsCSSRules.cpp
@@ -662,6 +662,7 @@ public:
   NS_IMETHOD  EnumerateRulesForwards(nsISupportsArrayEnumFunc aFunc, void * aData) const;
   NS_IMETHOD  DeleteStyleRuleAt(PRUint32 aIndex);
   NS_IMETHOD  InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules);
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule *aOld, nsICSSRule *aNew);
   
   // nsIDOMCSSRule interface
   NS_DECL_NSIDOMCSSRULE
@@ -872,6 +873,8 @@ CSSMediaRuleImpl::AppendStyleRule(nsICSSRule* aRule)
     aRule->SetStyleSheet(mSheet);
     aRule->SetParentRule(this);
     if (mSheet) {
+      // XXXldb Shouldn't we be using |WillDirty| and |DidDirty| (and
+      // shouldn't |SetModified| be removed?
       mSheet->SetModified(PR_TRUE);
     }
   }
@@ -952,6 +955,18 @@ CSSMediaRuleImpl::InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSMediaRuleImpl::ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  PRInt32 index = mRules->IndexOf(aOld);
+  NS_ENSURE_TRUE(index != -1, NS_ERROR_UNEXPECTED);
+  mRules->ReplaceElementAt(aNew, index);
+  aNew->SetStyleSheet(mSheet);
+  aNew->SetParentRule(this);
+  aOld->SetStyleSheet(nsnull);
+  aOld->SetParentRule(nsnull);
+  return NS_OK;
+}
 
 nsresult
 NS_NewCSSMediaRule(nsICSSMediaRule** aInstancePtrResult)
diff --git a/mozilla/content/html/style/src/nsCSSStyleRule.cpp b/mozilla/content/html/style/src/nsCSSStyleRule.cpp
index e72cabd41df..b428220ca60 100644
--- a/mozilla/content/html/style/src/nsCSSStyleRule.cpp
+++ b/mozilla/content/html/style/src/nsCSSStyleRule.cpp
@@ -854,7 +854,7 @@ CSSImportantRule::List(FILE* out, PRInt32 aIndent) const
 }
 #endif
 
-// -- nsDOMStyleRuleDeclaration -------------------------------
+// -- DOMCSSDeclarationImpl -------------------------------
 
 class DOMCSSDeclarationImpl : public nsDOMCSSDeclaration
 {
@@ -862,24 +862,14 @@ public:
   DOMCSSDeclarationImpl(nsICSSStyleRule *aRule);
   ~DOMCSSDeclarationImpl(void);
 
-  NS_IMETHOD RemoveProperty(const nsAString& aPropertyName, 
-                            nsAString& aReturn);
-
   virtual void DropReference(void);
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate);
-  virtual nsresult GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
-                                            nsICSSStyleSheet** aSheet,
-                                            nsIDocument** aDocument,
-                                            nsIURI** aURI,
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aURI,
                                             nsICSSLoader** aCSSLoader,
                                             nsICSSParser** aCSSParser);
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue);
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl);
   virtual nsresult GetParent(nsISupports **aParent);
+  virtual nsresult DeclarationChanged();
 
 protected:
   nsICSSStyleRule *mRule;
@@ -901,55 +891,6 @@ DOMCSSDeclarationImpl::~DOMCSSDeclarationImpl(void)
   MOZ_COUNT_DTOR(DOMCSSDeclarationImpl);
 }
 
-NS_IMETHODIMP
-DOMCSSDeclarationImpl::RemoveProperty(const nsAString& aPropertyName, 
-                                      nsAString& aReturn)
-{
-  aReturn.Truncate();
-
-  nsCSSDeclaration* decl;
-  nsresult rv = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (NS_SUCCEEDED(rv) && decl) {
-    nsCOMPtr<nsICSSStyleSheet> cssSheet;
-    nsCOMPtr<nsIDocument> owningDoc;
-    if (mRule) {
-      nsCOMPtr<nsIStyleSheet> sheet;
-      mRule->GetStyleSheet(*getter_AddRefs(sheet));
-      cssSheet = do_QueryInterface(sheet);
-      if (sheet) {
-        sheet->GetOwningDocument(*getter_AddRefs(owningDoc));
-      }
-    }
-    if (owningDoc) {
-      owningDoc->BeginUpdate();
-    }
-    nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
-
-    decl->GetValue(prop, aReturn);
-
-    rv = decl->RemoveProperty(prop);
-
-    if (NS_SUCCEEDED(rv)) {
-      if (cssSheet) {
-        cssSheet->SetModified(PR_TRUE);
-      }
-      if (owningDoc) {
-        owningDoc->StyleRuleChanged(cssSheet, mRule, nsCSSProps::kHintTable[prop]);
-      }
-    } else {
-      // If we tried to remove an invalid property or a property that wasn't 
-      //  set we simply return success and an empty string
-      rv = NS_OK;
-    }
-    if (owningDoc) {
-      owningDoc->EndUpdate();
-    }
-  }
-
-  return rv;
-}
-
 void 
 DOMCSSDeclarationImpl::DropReference(void)
 {
@@ -972,38 +913,34 @@ DOMCSSDeclarationImpl::GetCSSDeclaration(nsCSSDeclaration **aDecl,
 
 /*
  * This is a utility function.  It will only fail if it can't get a
- * parser.  This means it can return NS_OK without all of aSheet,
- *  aDocument, aURI, aCSSLoader being initialized
+ * parser.  This means it can return NS_OK without aURI or aCSSLoader
+ * being initialized.
  */
 nsresult
-DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
-                                                nsICSSStyleSheet** aSheet,
-                                                nsIDocument** aDocument,
-                                                nsIURI** aURI,
+DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsIURI** aURI,
                                                 nsICSSLoader** aCSSLoader,
                                                 nsICSSParser** aCSSParser)
 {
   // null out the out params since some of them may not get initialized below
-  *aSheet = nsnull;
-  *aDocument = nsnull;
   *aURI = nsnull;
   *aCSSLoader = nsnull;
   *aCSSParser = nsnull;
   nsresult result;
   nsCOMPtr<nsIStyleSheet> sheet;
-  if (aRule) {
-    aRule->GetStyleSheet(*getter_AddRefs(sheet));
+  if (mRule) {
+    mRule->GetStyleSheet(*getter_AddRefs(sheet));
     if (sheet) {
-      CallQueryInterface(sheet, aSheet);
-      sheet->GetOwningDocument(*aDocument);
       sheet->GetURL(*aURI);
+      nsCOMPtr<nsIDocument> document;
+      sheet->GetOwningDocument(*getter_AddRefs(document));
+      nsCOMPtr<nsIHTMLContentContainer> htmlContainer =
+        do_QueryInterface(document);
+      if (htmlContainer) {
+        htmlContainer->GetCSSLoader(*aCSSLoader);
+        NS_ASSERTION(*aCSSLoader, "Document with no CSS loader!");
+      }
     }
   }
-  nsCOMPtr<nsIHTMLContentContainer> htmlContainer(do_QueryInterface(*aDocument));
-  if (htmlContainer) {
-    htmlContainer->GetCSSLoader(*aCSSLoader);
-  }
-  NS_ASSERTION(*aCSSLoader || !*aDocument, "Document with no CSS loader!");
   if (*aCSSLoader) {
     result = (*aCSSLoader)->GetParserFor(nsnull, aCSSParser);
   } else {
@@ -1013,99 +950,6 @@ DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
   return result;
 }
 
-nsresult
-DOMCSSDeclarationImpl::ParsePropertyValue(const nsAString& aPropName,
-                                          const nsAString& aPropValue)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-  if (!decl) {
-    return result;
-  }
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-  nsCOMPtr<nsICSSStyleSheet> cssSheet;
-  nsCOMPtr<nsIDocument> owningDoc;
-  result = GetCSSParsingEnvironment(mRule,
-                                    getter_AddRefs(cssSheet),
-                                    getter_AddRefs(owningDoc),
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-
-  if (NS_FAILED(result)) {
-    return result;
-  }
-  
-  nsChangeHint hint;
-  if (owningDoc) {
-    owningDoc->BeginUpdate();
-  }
-  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl, &hint);
-  if (NS_SUCCEEDED(result)) {
-    if (cssSheet) {
-      cssSheet->SetModified(PR_TRUE);
-    }
-    if (owningDoc) {
-      owningDoc->StyleRuleChanged(cssSheet, mRule, hint);
-      owningDoc->EndUpdate();
-    }
-  }
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
-nsresult 
-DOMCSSDeclarationImpl::ParseDeclaration(const nsAString& aDecl,
-                                        PRBool aParseOnlyOneDecl,
-                                        PRBool aClearOldDecl)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (decl) {
-    nsCOMPtr<nsICSSLoader> cssLoader;
-    nsCOMPtr<nsICSSParser> cssParser;
-    nsCOMPtr<nsIURI> baseURI;
-    nsCOMPtr<nsICSSStyleSheet> cssSheet;
-    nsCOMPtr<nsIDocument> owningDoc;
-
-    result = GetCSSParsingEnvironment(mRule,
-                                      getter_AddRefs(cssSheet),
-                                      getter_AddRefs(owningDoc),
-                                      getter_AddRefs(baseURI),
-                                      getter_AddRefs(cssLoader),
-                                      getter_AddRefs(cssParser));
-
-    if (NS_SUCCEEDED(result)) {
-      nsChangeHint hint;
-      result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
-                                                    aParseOnlyOneDecl, &hint,
-                                                    aClearOldDecl);
-
-      if (NS_SUCCEEDED(result)) {
-        if (cssSheet) {
-          cssSheet->SetModified(PR_TRUE);
-        }
-        if (owningDoc) {
-          owningDoc->StyleRuleChanged(cssSheet, mRule, hint);
-        }
-      }
-      if (cssLoader) {
-        cssLoader->RecycleParser(cssParser);
-      }
-    }
-  }
-
-  return result;
-}
-
-
-
 nsresult 
 DOMCSSDeclarationImpl::GetParent(nsISupports **aParent)
 {
@@ -1120,6 +964,37 @@ DOMCSSDeclarationImpl::GetParent(nsISupports **aParent)
   return NS_OK;
 }
 
+nsresult
+DOMCSSDeclarationImpl::DeclarationChanged()
+{
+  NS_PRECONDITION(mRule,
+         "can only be called when |GetCSSDeclaration| returned a declaration");
+
+  nsCOMPtr<nsIDocument> owningDoc;
+  nsCOMPtr<nsIStyleSheet> sheet;
+  mRule->GetStyleSheet(*getter_AddRefs(sheet));
+  if (sheet) {
+    sheet->GetOwningDocument(*getter_AddRefs(owningDoc));
+  }
+
+  if (owningDoc) {
+    // XXXldb Do we need to bother with this?  We're now doing it in
+    // more places than we used to, but it probably doesn't matter...
+    owningDoc->BeginUpdate();
+  }
+
+  nsCOMPtr<nsICSSStyleRule> oldRule = mRule;
+  mRule = oldRule->DeclarationChanged(PR_TRUE).get();
+  nsrefcnt cnt = mRule->Release();
+  NS_ASSERTION(cnt != 0, "container didn't take ownership");
+
+  if (owningDoc) {
+    owningDoc->StyleRuleChanged(sheet, oldRule, mRule);
+    owningDoc->EndUpdate();
+  }
+  return NS_OK;
+}
+
 // -- nsCSSStyleRule -------------------------------
 
 class CSSStyleRuleImpl : public nsCSSRule,
@@ -1127,8 +1002,15 @@ class CSSStyleRuleImpl : public nsCSSRule,
                          public nsIDOMCSSStyleRule
 {
 public:
-  CSSStyleRuleImpl(nsCSSSelectorList* aSelector);
+  CSSStyleRuleImpl(nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration *aDeclaration);
+private:
+  // for |Clone|
   CSSStyleRuleImpl(const CSSStyleRuleImpl& aCopy); 
+  // for |DeclarationChanged|
+  CSSStyleRuleImpl(CSSStyleRuleImpl& aCopy,
+                   nsCSSDeclaration *aDeclaration); 
+public:
 
   NS_DECL_ISUPPORTS_INHERITED
 
@@ -1138,7 +1020,6 @@ public:
   virtual void SetLineNumber(PRUint32 aLineNumber);
 
   virtual nsCSSDeclaration* GetDeclaration(void) const;
-  virtual void SetDeclaration(nsCSSDeclaration* aDeclaration);
 
   virtual already_AddRefed<nsIStyleRule> GetImportantRule(void);
 
@@ -1153,6 +1034,9 @@ public:
   NS_IMETHOD GetType(PRInt32& aType) const;
   NS_IMETHOD Clone(nsICSSRule*& aClone) const;
 
+  virtual already_AddRefed<nsICSSStyleRule>
+    DeclarationChanged(PRBool aHandleContainer);
+
   // The new mapping function.
   NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData);
 
@@ -1181,30 +1065,50 @@ protected:
   PRUint32                mLineNumber;
 };
 
-CSSStyleRuleImpl::CSSStyleRuleImpl(nsCSSSelectorList* aSelector)
+CSSStyleRuleImpl::CSSStyleRuleImpl(nsCSSSelectorList* aSelector,
+                                   nsCSSDeclaration* aDeclaration)
   : nsCSSRule(),
-    mSelector(aSelector), mDeclaration(nsnull), 
+    mSelector(aSelector),
+    mDeclaration(aDeclaration), 
     mImportantRule(nsnull),
     mDOMDeclaration(nsnull)
 {
+  if (mDeclaration)
+    mDeclaration->AddRef();
 }
 
+// for |Clone|
 CSSStyleRuleImpl::CSSStyleRuleImpl(const CSSStyleRuleImpl& aCopy)
   : nsCSSRule(aCopy),
     mSelector(aCopy.mSelector ? aCopy.mSelector->Clone() : nsnull),
-    mDeclaration(nsnull),
+    mDeclaration(aCopy.mDeclaration ? aCopy.mDeclaration->Clone() : nsnull),
     mImportantRule(nsnull),
     mDOMDeclaration(nsnull)
 {
-  if (aCopy.mDeclaration) {
-    mDeclaration = aCopy.mDeclaration->Clone();
-    if (nsnull != mDeclaration) {
-      mDeclaration->AddRef();
-    }
-  }
+  if (mDeclaration)
+    mDeclaration->AddRef();
   // rest is constructed lazily on existing data
 }
 
+// for |DeclarationChanged|
+CSSStyleRuleImpl::CSSStyleRuleImpl(CSSStyleRuleImpl& aCopy,
+                                   nsCSSDeclaration* aDeclaration)
+  : nsCSSRule(aCopy),
+    mSelector(aCopy.mSelector),
+    mDeclaration(aDeclaration),
+    mImportantRule(nsnull),
+    mDOMDeclaration(aCopy.mDOMDeclaration)
+{
+  // The DOM declaration is replacing |aCopy| with |this|, so transfer
+  // the reverse pointer as well.
+  aCopy.mDOMDeclaration = nsnull;
+
+  // Transfer ownership of selector and declaration:
+  NS_ASSERTION(aDeclaration == aCopy.mDeclaration, "declaration mismatch");
+  aCopy.mSelector = nsnull;
+  aCopy.mDeclaration = nsnull;
+}
+
 
 CSSStyleRuleImpl::~CSSStyleRuleImpl(void)
 {
@@ -1259,20 +1163,7 @@ void CSSStyleRuleImpl::SetLineNumber(PRUint32 aLineNumber)
 
 nsCSSDeclaration* CSSStyleRuleImpl::GetDeclaration(void) const
 {
-  nsCSSDeclaration* result = mDeclaration;
-  return result;
-}
-
-void CSSStyleRuleImpl::SetDeclaration(nsCSSDeclaration* aDeclaration)
-{
-  if (mDeclaration != aDeclaration) {
-    NS_IF_RELEASE(mImportantRule); 
-    if (nsnull != mDeclaration) {
-      mDeclaration->Release();
-    }
-    mDeclaration = aDeclaration;
-    mDeclaration->AddRef();
-  }
+  return mDeclaration;
 }
 
 already_AddRefed<nsIStyleRule> CSSStyleRuleImpl::GetImportantRule(void)
@@ -1326,11 +1217,32 @@ NS_IMETHODIMP
 CSSStyleRuleImpl::Clone(nsICSSRule*& aClone) const
 {
   CSSStyleRuleImpl* clone = new CSSStyleRuleImpl(*this);
-  if (clone) {
-    return CallQueryInterface(clone, &aClone);
+  if (!clone) {
+    aClone = nsnull;
+    return NS_ERROR_OUT_OF_MEMORY;
   }
-  aClone = nsnull;
-  return NS_ERROR_OUT_OF_MEMORY;
+  return CallQueryInterface(clone, &aClone);
+}
+
+/* virtual */ already_AddRefed<nsICSSStyleRule>
+CSSStyleRuleImpl::DeclarationChanged(PRBool aHandleContainer)
+{
+  CSSStyleRuleImpl* clone = new CSSStyleRuleImpl(*this, mDeclaration);
+  if (!clone) {
+    return nsnull;
+  }
+
+  NS_ADDREF(clone); // for return
+
+  if (aHandleContainer) {
+    if (mParentRule) {
+      mSheet->ReplaceRuleInGroup(mParentRule, this, clone);
+    } else {
+      mSheet->ReplaceStyleRule(this, clone);
+    }
+  }
+
+  return clone;
 }
 
 NS_IMETHODIMP
@@ -1457,13 +1369,10 @@ CSSStyleRuleImpl::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
 
 nsresult
 NS_NewCSSStyleRule(nsICSSStyleRule** aInstancePtrResult,
-                   nsCSSSelectorList* aSelector)
+                   nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration* aDeclaration)
 {
-  if (aInstancePtrResult == nsnull) {
-    return NS_ERROR_NULL_POINTER;
-  }
-
-  CSSStyleRuleImpl *it = new CSSStyleRuleImpl(aSelector);
+  CSSStyleRuleImpl *it = new CSSStyleRuleImpl(aSelector, aDeclaration);
   if (!it) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
diff --git a/mozilla/content/html/style/src/nsCSSStyleSheet.cpp b/mozilla/content/html/style/src/nsCSSStyleSheet.cpp
index d93fa334b6b..9fc2ff1945c 100644
--- a/mozilla/content/html/style/src/nsCSSStyleSheet.cpp
+++ b/mozilla/content/html/style/src/nsCSSStyleSheet.cpp
@@ -819,6 +819,7 @@ public:
   NS_IMETHOD ClearMedia(void);
   NS_IMETHOD DeleteRuleFromGroup(nsICSSGroupRule* aGroup, PRUint32 aIndex);
   NS_IMETHOD InsertRuleIntoGroup(const nsAString& aRule, nsICSSGroupRule* aGroup, PRUint32 aIndex, PRUint32* _retval);
+  NS_IMETHOD ReplaceRuleInGroup(nsICSSGroupRule* aGroup, nsICSSRule* aOld, nsICSSRule* aNew);
   
   NS_IMETHOD GetApplicable(PRBool& aApplicable) const;
   
@@ -847,6 +848,7 @@ public:
   // XXX do these belong here or are they generic?
   NS_IMETHOD PrependStyleRule(nsICSSRule* aRule);
   NS_IMETHOD AppendStyleRule(nsICSSRule* aRule);
+  NS_IMETHOD ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew);
 
   NS_IMETHOD  StyleRuleCount(PRInt32& aCount) const;
   NS_IMETHOD  GetStyleRuleAt(PRInt32 aIndex, nsICSSRule*& aRule) const;
@@ -1354,7 +1356,8 @@ DOMMediaListImpl::EndMediaChange(void)
     mStyleSheet->DidDirty();
     rv = mStyleSheet->GetOwningDocument(*getter_AddRefs(doc));
     NS_ENSURE_SUCCESS(rv, rv);
-    rv = doc->StyleRuleChanged(mStyleSheet, nsnull, NS_STYLE_HINT_RECONSTRUCT_ALL);
+    // XXXldb Pass something meaningful?
+    rv = doc->StyleRuleChanged(mStyleSheet, nsnull, nsnull);
     NS_ENSURE_SUCCESS(rv, rv);
     rv = doc->EndUpdate();
     NS_ENSURE_SUCCESS(rv, rv);
@@ -2159,6 +2162,32 @@ CSSStyleSheetImpl::AppendStyleRule(nsICSSRule* aRule)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSStyleSheetImpl::ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  NS_PRECONDITION(mInner->mOrderedRules, "can't have old rule");
+  NS_PRECONDITION(mInner && mInner->mComplete,
+                  "No replacing in an incomplete sheet!");
+
+  if (NS_SUCCEEDED(WillDirty())) {
+    PRInt32 index = mInner->mOrderedRules->IndexOf(aOld);
+    NS_ENSURE_TRUE(index != -1, NS_ERROR_UNEXPECTED);
+    mInner->mOrderedRules->ReplaceElementAt(aNew, index);
+
+    aNew->SetStyleSheet(this);
+    aOld->SetStyleSheet(nsnull);
+    DidDirty();
+#ifdef DEBUG
+    PRInt32 type = nsICSSRule::UNKNOWN_RULE;
+    aNew->GetType(type);
+    NS_ASSERTION(nsICSSRule::NAMESPACE_RULE != type, "not yet implemented");
+    aOld->GetType(type);
+    NS_ASSERTION(nsICSSRule::NAMESPACE_RULE != type, "not yet implemented");
+#endif
+  }
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 CSSStyleSheetImpl::StyleRuleCount(PRInt32& aCount) const
 {
@@ -2981,6 +3010,29 @@ CSSStyleSheetImpl::InsertRuleIntoGroup(const nsAString & aRule, nsICSSGroupRule*
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSStyleSheetImpl::ReplaceRuleInGroup(nsICSSGroupRule* aGroup,
+                                      nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  nsresult result;
+  NS_PRECONDITION(mInner && mInner->mComplete,
+                  "No replacing in an incomplete sheet!");
+#ifdef DEBUG
+  {
+    nsCOMPtr<nsIDOMCSSRule> domGroup(do_QueryInterface(aGroup));
+    nsCOMPtr<nsIDOMCSSStyleSheet> groupSheet;
+    domGroup->GetParentStyleSheet(getter_AddRefs(groupSheet));
+    NS_ASSERTION(this == groupSheet, "group doesn't belong to this sheet");
+  }
+#endif
+  result = WillDirty();
+  NS_ENSURE_SUCCESS(result, result);
+
+  result = aGroup->ReplaceStyleRule(aOld, aNew);
+  DidDirty();
+  return result;
+}
+
 // nsICSSLoaderObserver implementation
 NS_IMETHODIMP
 CSSStyleSheetImpl::StyleSheetLoaded(nsICSSStyleSheet*aSheet, PRBool aNotify)
diff --git a/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.cpp b/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.cpp
index ddadc3b3ea1..ca1e51a4d7c 100644
--- a/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.cpp
+++ b/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.cpp
@@ -68,35 +68,6 @@ nsDOMCSSAttributeDeclaration::~nsDOMCSSAttributeDeclaration()
   MOZ_COUNT_DTOR(nsDOMCSSAttributeDeclaration);
 }
 
-NS_IMETHODIMP
-nsDOMCSSAttributeDeclaration::RemoveProperty(const nsAString& aPropertyName,
-                                             nsAString& aReturn)
-{
-  aReturn.Truncate();
-
-  nsCSSDeclaration* decl;
-  nsresult rv = GetCSSDeclaration(&decl, PR_FALSE);
-
-  if (NS_SUCCEEDED(rv) && decl) {
-    nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
-
-    decl->GetValue(prop, aReturn);
-
-    rv = decl->RemoveProperty(prop);
-
-    if (NS_SUCCEEDED(rv)) {
-      rv = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-    } else {
-      // RemoveProperty will throw in all sorts of situations -- eg if
-      // the property is a shorthand one.  Do not propagate its return
-      // value to callers.
-      rv = NS_OK;
-    }
-  }
-
-  return rv;
-}
-
 void
 nsDOMCSSAttributeDeclaration::DropReference()
 {
@@ -104,26 +75,25 @@ nsDOMCSSAttributeDeclaration::DropReference()
 }
 
 nsresult
-nsDOMCSSAttributeDeclaration::SetCSSDeclaration(nsCSSDeclaration* aDecl,
-                                                PRBool aNotify,
-                                                PRBool aDeclOwnedByRule)
+nsDOMCSSAttributeDeclaration::DeclarationChanged()
 {
   NS_ASSERTION(mContent, "Must have content node to set the decl!");
-  NS_PRECONDITION(aDecl, "Null decl!");
-    
-  nsCOMPtr<nsICSSStyleRule> cssRule;
-  nsresult rv = NS_NewCSSStyleRule(getter_AddRefs(cssRule), nsnull);
-  if (NS_FAILED(rv)) {
-    if (!aDeclOwnedByRule) {
-      aDecl->RuleAbort();
-    }
-    return rv;
+  nsHTMLValue val;
+  nsresult rv = mContent->GetHTMLAttribute(nsHTMLAtoms::style, val);
+  NS_ASSERTION(rv == NS_CONTENT_ATTR_HAS_VALUE &&
+               eHTMLUnit_ISupports == val.GetUnit(),
+               "content must have rule");
+  nsCOMPtr<nsICSSStyleRule> oldRule =
+    do_QueryInterface(nsCOMPtr<nsISupports>(val.GetISupportsValue()));
+
+  nsCOMPtr<nsICSSStyleRule> newRule = oldRule->DeclarationChanged(PR_FALSE);
+  if (!newRule) {
+    return NS_ERROR_OUT_OF_MEMORY;
   }
     
-  cssRule->SetDeclaration(aDecl);
   return mContent->SetHTMLAttribute(nsHTMLAtoms::style,
-                                    nsHTMLValue(cssRule),
-                                    aNotify);
+                                    nsHTMLValue(newRule),
+                                    PR_TRUE);
 }
 
 nsresult
@@ -152,7 +122,17 @@ nsDOMCSSAttributeDeclaration::GetCSSDeclaration(nsCSSDeclaration **aDecl,
         decl->RuleAbort();
         return NS_ERROR_OUT_OF_MEMORY;
       }
-      result = SetCSSDeclaration(decl, PR_FALSE, PR_FALSE);
+
+      nsCOMPtr<nsICSSStyleRule> cssRule;
+      result = NS_NewCSSStyleRule(getter_AddRefs(cssRule), nsnull, decl);
+      if (NS_FAILED(result)) {
+        decl->RuleAbort();
+        return result;
+      }
+        
+      result = mContent->SetHTMLAttribute(nsHTMLAtoms::style,
+                                          nsHTMLValue(cssRule),
+                                          PR_FALSE);
       if (NS_SUCCEEDED(result)) {
         *aDecl = decl;
       }
@@ -165,22 +145,21 @@ nsDOMCSSAttributeDeclaration::GetCSSDeclaration(nsCSSDeclaration **aDecl,
 /*
  * This is a utility function.  It will only fail if it can't get a
  * parser.  This means it can return NS_OK without aURI or aCSSLoader
- * being initialized
+ * being initialized.
  */
 nsresult
-nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIContent* aContent,
-                                                       nsIURI** aBaseURI,
+nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIURI** aBaseURI,
                                                        nsICSSLoader** aCSSLoader,
                                                        nsICSSParser** aCSSParser)
 {
-  NS_ASSERTION(aContent, "Something is severely broken -- there should be an nsIContent here!");
+  NS_ASSERTION(mContent, "Something is severely broken -- there should be an nsIContent here!");
   // null out the out params since some of them may not get initialized below
   *aBaseURI = nsnull;
   *aCSSLoader = nsnull;
   *aCSSParser = nsnull;
   
   nsCOMPtr<nsINodeInfo> nodeInfo;
-  nsresult result = aContent->GetNodeInfo(getter_AddRefs(nodeInfo));
+  nsresult result = mContent->GetNodeInfo(getter_AddRefs(nodeInfo));
   if (NS_FAILED(result)) {
     return result;
   }
@@ -214,85 +193,6 @@ nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIContent* aContent,
   return NS_OK;
 }
 
-nsresult
-nsDOMCSSAttributeDeclaration::ParsePropertyValue(const nsAString& aPropName,
-                                                 const nsAString& aPropValue)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (!decl) {
-    return result;
-  }
-  
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-  
-  result = GetCSSParsingEnvironment(mContent,
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-  if (NS_FAILED(result)) {
-    return result;
-  }
-
-  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
-  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl,
-                                    &uselessHint);
-  if (NS_SUCCEEDED(result)) {
-    result = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-  }
-
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
-nsresult
-nsDOMCSSAttributeDeclaration::ParseDeclaration(const nsAString& aDecl,
-                                               PRBool aParseOnlyOneDecl,
-                                               PRBool aClearOldDecl)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (!decl) {
-    return result;
-  }
-
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-
-  result = GetCSSParsingEnvironment(mContent,
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-
-  if (NS_FAILED(result)) {
-    return result;
-  }
-
-  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
-  result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
-                                                aParseOnlyOneDecl,
-                                                &uselessHint,
-                                                aClearOldDecl);
-  
-  if (NS_SUCCEEDED(result)) {
-    result = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-  }
-
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
 nsresult
 nsDOMCSSAttributeDeclaration::GetParent(nsISupports **aParent)
 {
diff --git a/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.h b/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.h
index 1d2abb93c0e..97575e4e098 100644
--- a/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.h
+++ b/mozilla/content/html/style/src/nsDOMCSSAttrDeclaration.h
@@ -55,28 +55,18 @@ public:
   nsDOMCSSAttributeDeclaration(nsIHTMLContent *aContent);
   ~nsDOMCSSAttributeDeclaration();
 
-  NS_IMETHOD RemoveProperty(const nsAString& aPropertyName,
-                            nsAString& aReturn);
-
   virtual void DropReference();
   // If GetCSSDeclaration returns non-null, then the decl it returns
   // is owned by our current style rule.
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate);
-  virtual nsresult GetCSSParsingEnvironment(nsIContent* aContent,
-                                            nsIURI** aBaseURI,
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aBaseURI,
                                             nsICSSLoader** aCSSLoader,
                                             nsICSSParser** aCSSParser);
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue);
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl);
   virtual nsresult GetParent(nsISupports **aParent);
 
 protected:
-  nsresult SetCSSDeclaration(nsCSSDeclaration* aDecl, PRBool aNotify,
-                             PRBool aDeclOwnedByRule);
+  virtual nsresult DeclarationChanged();
   
   nsIHTMLContent *mContent;
 };
diff --git a/mozilla/content/html/style/src/nsDOMCSSDeclaration.cpp b/mozilla/content/html/style/src/nsDOMCSSDeclaration.cpp
index 7f7f861b7f2..4ccba2920e5 100644
--- a/mozilla/content/html/style/src/nsDOMCSSDeclaration.cpp
+++ b/mozilla/content/html/style/src/nsDOMCSSDeclaration.cpp
@@ -39,6 +39,7 @@
 #include "nsDOMCSSDeclaration.h"
 #include "nsIDOMCSSRule.h"
 #include "nsICSSParser.h"
+#include "nsICSSLoader.h"
 #include "nsIStyleRule.h"
 #include "nsCSSDeclaration.h"
 #include "nsCSSProps.h"
@@ -138,9 +139,10 @@ nsDOMCSSDeclaration::GetLength(PRUint32* aLength)
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
  
-  *aLength = 0;
-  if ((NS_OK == result) && (nsnull != decl)) {
+  if (decl) {
     *aLength = decl->Count();
+  } else {
+    *aLength = 0;
   }
 
   return result;
@@ -182,7 +184,7 @@ nsDOMCSSDeclaration::Item(PRUint32 aIndex, nsAString& aReturn)
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
 
   aReturn.SetLength(0);
-  if ((NS_OK == result) && (nsnull != decl)) {
+  if (decl) {
     result = decl->GetNthProperty(aIndex, aReturn);
   }
 
@@ -197,8 +199,8 @@ nsDOMCSSDeclaration::GetPropertyValue(const nsAString& aPropertyName,
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
 
-  aReturn.SetLength(0);
-  if ((NS_OK == result) && (nsnull != decl)) {
+  aReturn.Truncate();
+  if (decl) {
     result = decl->GetValue(aPropertyName, aReturn);
   }
 
@@ -211,18 +213,11 @@ nsDOMCSSDeclaration::GetPropertyPriority(const nsAString& aPropertyName,
 {
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
-  PRBool isImportant = PR_FALSE;
 
-  if ((NS_OK == result) && (nsnull != decl)) {
-    isImportant = decl->GetValueIsImportant(aPropertyName);
-  }
-
-  if ((NS_OK == result) && isImportant) {
+  aReturn.Truncate();
+  if (decl && decl->GetValueIsImportant(aPropertyName)) {
     aReturn.Assign(NS_LITERAL_STRING("important"));    
   }
-  else {
-    aReturn.SetLength(0);
-  }
 
   return result;
 }
@@ -252,6 +247,112 @@ nsDOMCSSDeclaration::SetProperty(const nsAString& aPropertyName,
                           PR_TRUE, PR_FALSE);
 }
 
+NS_IMETHODIMP
+nsDOMCSSDeclaration::RemoveProperty(const nsAString& aPropertyName,
+                                    nsAString& aReturn)
+{
+  aReturn.Truncate();
+
+  nsCSSDeclaration* decl;
+  nsresult rv = GetCSSDeclaration(&decl, PR_FALSE);
+  if (!decl) {
+    return rv;
+  }
+
+  nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
+
+  decl->GetValue(prop, aReturn);
+
+  rv = decl->RemoveProperty(prop);
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = DeclarationChanged();
+  } else {
+    // RemoveProperty used to throw in all sorts of situations -- e.g.
+    // if the property was a shorthand one.  Do not propagate its return
+    // value to callers.  (XXX or should we propagate it again now?)
+    rv = NS_OK;
+  }
+
+  return rv;
+}
+
+nsresult
+nsDOMCSSDeclaration::ParsePropertyValue(const nsAString& aPropName,
+                                        const nsAString& aPropValue)
+{
+  nsCSSDeclaration* decl;
+  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
+  if (!decl) {
+    return result;
+  }
+  
+  nsCOMPtr<nsICSSLoader> cssLoader;
+  nsCOMPtr<nsICSSParser> cssParser;
+  nsCOMPtr<nsIURI> baseURI;
+  
+  result = GetCSSParsingEnvironment(getter_AddRefs(baseURI),
+                                    getter_AddRefs(cssLoader),
+                                    getter_AddRefs(cssParser));
+  if (NS_FAILED(result)) {
+    return result;
+  }
+
+  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
+  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl,
+                                    &uselessHint);
+  if (NS_SUCCEEDED(result)) {
+    result = DeclarationChanged();
+  }
+
+  if (cssLoader) {
+    cssLoader->RecycleParser(cssParser);
+  }
+
+  return result;
+}
+
+nsresult
+nsDOMCSSDeclaration::ParseDeclaration(const nsAString& aDecl,
+                                      PRBool aParseOnlyOneDecl,
+                                      PRBool aClearOldDecl)
+{
+  nsCSSDeclaration* decl;
+  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
+  if (!decl) {
+    return result;
+  }
+
+  nsCOMPtr<nsICSSLoader> cssLoader;
+  nsCOMPtr<nsICSSParser> cssParser;
+  nsCOMPtr<nsIURI> baseURI;
+
+  result = GetCSSParsingEnvironment(getter_AddRefs(baseURI),
+                                    getter_AddRefs(cssLoader),
+                                    getter_AddRefs(cssParser));
+
+  if (NS_FAILED(result)) {
+    return result;
+  }
+
+  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
+  result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
+                                                aParseOnlyOneDecl,
+                                                &uselessHint,
+                                                aClearOldDecl);
+  
+  if (NS_SUCCEEDED(result)) {
+    result = DeclarationChanged();
+  }
+
+  if (cssLoader) {
+    cssLoader->RecycleParser(cssParser);
+  }
+
+  return result;
+}
+
+
 //////////////////////////////////////////////////////////////////////////////
 
 CSS2PropertiesTearoff::CSS2PropertiesTearoff(nsISupports *aOuter)
diff --git a/mozilla/content/html/style/src/nsDOMCSSDeclaration.h b/mozilla/content/html/style/src/nsDOMCSSDeclaration.h
index 7f0e19e2a05..9421f67683e 100644
--- a/mozilla/content/html/style/src/nsDOMCSSDeclaration.h
+++ b/mozilla/content/html/style/src/nsDOMCSSDeclaration.h
@@ -47,6 +47,7 @@
 
 class nsCSSDeclaration;
 class nsICSSParser;
+class nsICSSLoader;
 class nsIURI;
 
 class nsDOMCSSDeclaration : public nsIDOMCSSStyleDeclaration
@@ -56,35 +57,28 @@ public:
 
   NS_DECL_ISUPPORTS
 
-  // NS_DECL_IDOMCSSSTYLEDECLARATION
-  NS_IMETHOD    GetCssText(nsAString& aCssText);
-  NS_IMETHOD    SetCssText(const nsAString& aCssText);
-  NS_IMETHOD    GetLength(PRUint32* aLength);
-  NS_IMETHOD    GetParentRule(nsIDOMCSSRule** aParentRule);
-  NS_IMETHOD    GetPropertyValue(const nsAString& aPropertyName,
-                                 nsAString& aReturn);
-  NS_IMETHOD    GetPropertyCSSValue(const nsAString& aPropertyName,
-                                    nsIDOMCSSValue** aReturn);
-  NS_IMETHOD    RemoveProperty(const nsAString& aPropertyName,
-                               nsAString& aReturn) = 0;
-  NS_IMETHOD    GetPropertyPriority(const nsAString& aPropertyName,
-                                    nsAString& aReturn);
-  NS_IMETHOD    SetProperty(const nsAString& aPropertyName,
-                            const nsAString& aValue,
-                            const nsAString& aPriority);
-  NS_IMETHOD    Item(PRUint32 aIndex, nsAString& aReturn);
-
+  NS_DECL_NSIDOMCSSSTYLEDECLARATION
 
   virtual void DropReference() = 0;
-  // XXX DeCOMify this, so that |nsCSSDeclaration*| is the return type.
+protected:
+  // Always fills in the out parameter, even on failure, and if the out
+  // parameter is null the nsresult will be the correct thing to
+  // propagate.
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate) = 0;
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue) = 0;
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl) = 0;
   virtual nsresult GetParent(nsISupports **aParent) = 0;
+  virtual nsresult DeclarationChanged() = 0;
+  
+  // This will only fail if it can't get a parser.  This means it can
+  // return NS_OK without aURI or aCSSLoader being initialized.
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aBaseURI,
+                                            nsICSSLoader** aCSSLoader,
+                                            nsICSSParser** aCSSParser) = 0;
+
+  nsresult ParsePropertyValue(const nsAString& aPropName,
+                              const nsAString& aPropValue);
+  nsresult ParseDeclaration(const nsAString& aDecl,
+                            PRBool aParseOnlyOneDecl, PRBool aClearOldDecl);
   
 protected:
   virtual ~nsDOMCSSDeclaration();
diff --git a/mozilla/content/html/style/src/nsICSSGroupRule.h b/mozilla/content/html/style/src/nsICSSGroupRule.h
index f76a34bb920..210f8287fdc 100644
--- a/mozilla/content/html/style/src/nsICSSGroupRule.h
+++ b/mozilla/content/html/style/src/nsICSSGroupRule.h
@@ -59,14 +59,13 @@ public:
   NS_IMETHOD  EnumerateRulesForwards(nsISupportsArrayEnumFunc aFunc, void * aData) const = 0;
 
   /*
-   * The next two methods (DeleteStyleRuleAt and InsertStyleRulesAt)
-   * should never be called unless you have first called WillDirty()
-   * on the parent stylesheet.  After they are called, DidDirty()
-   * needs to be called on the sheet
+   * The next three methods should never be called unless you have first
+   * called WillDirty() on the parent stylesheet.  After they are
+   * called, DidDirty() needs to be called on the sheet.
    */
   NS_IMETHOD  DeleteStyleRuleAt(PRUint32 aIndex) = 0;
   NS_IMETHOD  InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules) = 0;
-
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew) = 0;
    
 };
 
diff --git a/mozilla/content/html/style/src/nsICSSStyleRule.h b/mozilla/content/html/style/src/nsICSSStyleRule.h
index c19044afac5..94afae748e4 100644
--- a/mozilla/content/html/style/src/nsICSSStyleRule.h
+++ b/mozilla/content/html/style/src/nsICSSStyleRule.h
@@ -201,7 +201,18 @@ public:
   virtual void SetLineNumber(PRUint32 aLineNumber) = 0;
 
   virtual nsCSSDeclaration* GetDeclaration(void) const = 0;
-  virtual void SetDeclaration(nsCSSDeclaration* aDeclaration) = 0;
+
+  /**
+   * Return a new |nsIStyleRule| instance that replaces the current one,
+   * due to a change in the |nsCSSDeclaration|.  Due to the
+   * |nsIStyleRule| contract of immutability, this must be called if the
+   * declaration is modified.
+   *
+   * |DeclarationChanged| handles replacing the object in the container
+   * sheet or group rule if |aHandleContainer| is true.
+   */
+  virtual already_AddRefed<nsICSSStyleRule>
+    DeclarationChanged(PRBool aHandleContainer) = 0;
 
   virtual already_AddRefed<nsIStyleRule> GetImportantRule(void) = 0;
 
@@ -211,6 +222,7 @@ public:
 
 nsresult
 NS_NewCSSStyleRule(nsICSSStyleRule** aInstancePtrResult,
-                   nsCSSSelectorList* aSelector);
+                   nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration* aDeclaration);
 
 #endif /* nsICSSStyleRule_h___ */
diff --git a/mozilla/content/shared/public/nsRuleNode.h b/mozilla/content/shared/public/nsRuleNode.h
index b5df7848fdd..c2532afc8cb 100644
--- a/mozilla/content/shared/public/nsRuleNode.h
+++ b/mozilla/content/shared/public/nsRuleNode.h
@@ -410,8 +410,7 @@ protected:
 
   const nsStyleStruct* WalkRuleTree(const nsStyleStructID aSID, nsStyleContext* aContext, 
                                     nsRuleData* aRuleData,
-                                    nsRuleDataStruct* aSpecificData,
-                                    PRBool aComputeData);
+                                    nsRuleDataStruct* aSpecificData);
 
   const nsStyleStruct* ComputeDisplayData(nsStyleStruct* aStartDisplay, const nsRuleDataStruct& aDisplayData, 
                                           nsStyleContext* aContext, nsRuleNode* aHighestNode,
@@ -504,31 +503,31 @@ protected:
   inline RuleDetail CheckSpecifiedProperties(const nsStyleStructID aSID, const nsRuleDataStruct& aRuleDataStruct);
 
   const nsStyleStruct* GetParentData(const nsStyleStructID aSID);
-  const nsStyleStruct* GetDisplayData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetVisibilityData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetFontData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetColorData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetBackgroundData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetMarginData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetBorderData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetPaddingData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetOutlineData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetListData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetPositionData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTableData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTableBorderData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetContentData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetQuotesData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTextData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTextResetData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetUserInterfaceData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetUIResetData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetXULData(nsStyleContext* aContext, PRBool aComputeData);
+  const nsStyleStruct* GetDisplayData(nsStyleContext* aContext);
+  const nsStyleStruct* GetVisibilityData(nsStyleContext* aContext);
+  const nsStyleStruct* GetFontData(nsStyleContext* aContext);
+  const nsStyleStruct* GetColorData(nsStyleContext* aContext);
+  const nsStyleStruct* GetBackgroundData(nsStyleContext* aContext);
+  const nsStyleStruct* GetMarginData(nsStyleContext* aContext);
+  const nsStyleStruct* GetBorderData(nsStyleContext* aContext);
+  const nsStyleStruct* GetPaddingData(nsStyleContext* aContext);
+  const nsStyleStruct* GetOutlineData(nsStyleContext* aContext);
+  const nsStyleStruct* GetListData(nsStyleContext* aContext);
+  const nsStyleStruct* GetPositionData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTableData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTableBorderData(nsStyleContext* aContext);
+  const nsStyleStruct* GetContentData(nsStyleContext* aContext);
+  const nsStyleStruct* GetQuotesData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTextData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTextResetData(nsStyleContext* aContext);
+  const nsStyleStruct* GetUserInterfaceData(nsStyleContext* aContext);
+  const nsStyleStruct* GetUIResetData(nsStyleContext* aContext);
+  const nsStyleStruct* GetXULData(nsStyleContext* aContext);
 #ifdef MOZ_SVG
-  const nsStyleStruct* GetSVGData(nsStyleContext* aContext, PRBool aComputeData);
+  const nsStyleStruct* GetSVGData(nsStyleContext* aContext);
 #endif
 
-  typedef const nsStyleStruct* (nsRuleNode::*GetStyleDataFn)(nsStyleContext*, PRBool);
+  typedef const nsStyleStruct* (nsRuleNode::*GetStyleDataFn)(nsStyleContext*);
   static GetStyleDataFn gGetStyleDataFn[];
 
 public:
@@ -557,8 +556,7 @@ public:
     return mPresContext;
   }
 
-  nsresult ClearCachedData(nsIStyleRule* aRule);
-  nsresult ClearCachedDataInSubtree(nsIStyleRule* aRule);
+  nsresult ClearStyleData();
   nsresult GetPresContext(nsIPresContext** aResult);
   nsresult PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched);
   const nsStyleStruct* GetStyleData(nsStyleStructID aSID, 
diff --git a/mozilla/content/shared/public/nsStyleContext.h b/mozilla/content/shared/public/nsStyleContext.h
index 1f480293632..be3629234e8 100644
--- a/mozilla/content/shared/public/nsStyleContext.h
+++ b/mozilla/content/shared/public/nsStyleContext.h
@@ -139,7 +139,7 @@ public:
 
   nsStyleStruct* GetUniqueStyleData(nsIPresContext* aPresContext, const nsStyleStructID& aSID);
 
-  void ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule);
+  void ClearStyleData(nsIPresContext* aPresContext);
 
   nsChangeHint CalcStyleDifference(nsStyleContext* aOther);
 
diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index 4c283a2f3b7..c7dcf639adc 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -10553,78 +10553,6 @@ nsCSSFrameConstructor::AttributeChanged(nsIPresContext* aPresContext,
   return result;
 }
 
-  // Style change notifications
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleChanged(nsIPresContext* aPresContext,
-                                        nsIStyleSheet* aStyleSheet,
-                                        nsIStyleRule* aStyleRule,
-                                        nsChangeHint aHint)
-{
-  nsresult result = NS_OK;
-  nsCOMPtr<nsIPresShell> shell;
-  aPresContext->GetShell(getter_AddRefs(shell));
-  nsIFrame* frame;
-  shell->GetRootFrame(&frame);
-
-  if (!frame) {
-    return NS_OK;
-  }
-
-  PRBool reframe = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                             | nsChangeHint_Unknown)) != 0;
-  PRBool restyle = (aHint & ~(nsChangeHint_AttrChange)) != 0;
-  // TBD: add "review" to update view?
-
-  if (restyle) {
-    nsCOMPtr<nsIStyleSet> set;
-    shell->GetStyleSet(getter_AddRefs(set));
-    set->ClearStyleData(aPresContext, aStyleRule);
-  }
-
-  if (reframe) {
-    result = ReconstructDocElementHierarchy(aPresContext);
-  }
-  else {
-    PRBool reflow = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                              | nsChangeHint_ReflowFrame | nsChangeHint_Unknown)) != 0;
-    PRBool renderOrSync = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                                    | nsChangeHint_ReflowFrame | nsChangeHint_RepaintFrame
-                                    | nsChangeHint_Unknown | nsChangeHint_SyncFrameView)) != 0;
-
-    // XXX hack, skip the root and scrolling frames
-    frame->FirstChild(aPresContext, nsnull, &frame);
-    frame->FirstChild(aPresContext, nsnull, &frame);
-    if (reflow) {
-      StyleChangeReflow(aPresContext, frame, nsnull);
-    }
-    if (renderOrSync) {
-      ApplyRenderingChangeToTree(aPresContext, frame, nsnull, aHint);
-    }
-  }
-
-  return result;
-}
-
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleAdded(nsIPresContext* aPresContext,
-                                      nsIStyleSheet* aStyleSheet,
-                                      nsIStyleRule* aStyleRule)
-{
-  // XXX TBI: should query rule for impact and do minimal work
-  ReconstructDocElementHierarchy(aPresContext);
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleRemoved(nsIPresContext* aPresContext,
-                                        nsIStyleSheet* aStyleSheet,
-                                        nsIStyleRule* aStyleRule)
-{
-  // XXX TBI: should query rule for impact and do minimal work
-  ReconstructDocElementHierarchy(aPresContext);
-  return NS_OK;
-}
-
 //STATIC
 void nsCSSFrameConstructor::GetAlternateTextFor(nsIContent* aContent,
                                                 nsIAtom*    aTag,  // content object's tag
diff --git a/mozilla/layout/base/nsCSSFrameConstructor.h b/mozilla/layout/base/nsCSSFrameConstructor.h
index ef3c7aa26c2..eedc0488573 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.h
+++ b/mozilla/layout/base/nsCSSFrameConstructor.h
@@ -141,20 +141,6 @@ public:
                               PRInt32         aModType, 
                               nsChangeHint    aHint);
 
-  // Style change notifications
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet*  aStyleSheet,
-                              nsIStyleRule*   aStyleRule,
-                              nsChangeHint    aHint);
-
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet*  aStyleSheet,
-                            nsIStyleRule*   aStyleRule);
-
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet*  aStyleSheet,
-                              nsIStyleRule*   aStyleRule);
-
   NS_IMETHOD ProcessRestyledFrames(nsStyleChangeList& aRestyleArray, 
                                    nsIPresContext*    aPresContext);
 
diff --git a/mozilla/layout/base/nsPresContext.cpp b/mozilla/layout/base/nsPresContext.cpp
index 0579fda8ab8..e49206ef765 100644
--- a/mozilla/layout/base/nsPresContext.cpp
+++ b/mozilla/layout/base/nsPresContext.cpp
@@ -576,7 +576,7 @@ nsPresContext::ClearStyleDataAndReflow()
     // Clear out all our style data.
     nsCOMPtr<nsIStyleSet> set;
     mShell->GetStyleSet(getter_AddRefs(set));
-    set->ClearStyleData(this, nsnull);
+    set->ClearStyleData(this);
 
     // Force a reflow of the root frame
     // XXX We really should only do a reflow if a preference that affects
diff --git a/mozilla/layout/base/nsPresShell.cpp b/mozilla/layout/base/nsPresShell.cpp
index ed8be251411..0d99dec0e0f 100644
--- a/mozilla/layout/base/nsPresShell.cpp
+++ b/mozilla/layout/base/nsPresShell.cpp
@@ -5657,15 +5657,10 @@ PresShell::StyleSheetApplicableStateChanged(nsIDocument *aDocument,
 NS_IMETHODIMP
 PresShell::StyleRuleChanged(nsIDocument *aDocument,
                             nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule,
-                            nsChangeHint aHint) 
+                            nsIStyleRule* aOldStyleRule,
+                            nsIStyleRule* aNewStyleRule)
 {
-  WillCauseReflow();
-  nsresult  rv = mStyleSet->StyleRuleChanged(mPresContext, aStyleSheet,
-                                             aStyleRule, aHint);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  return rv;
+  return ReconstructStyleData(PR_FALSE);
 }
 
 NS_IMETHODIMP
@@ -5673,18 +5668,6 @@ PresShell::StyleRuleAdded(nsIDocument *aDocument,
                           nsIStyleSheet* aStyleSheet,
                           nsIStyleRule* aStyleRule) 
 { 
-  WillCauseReflow();
-  nsresult rv = mStyleSet->StyleRuleAdded(mPresContext, aStyleSheet,
-                                          aStyleRule);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-
-  // We don't need to rebuild the
-  // rule tree, since no rule nodes have been rendered invalid by the
-  // addition of new rule content.  
   return ReconstructStyleData(PR_FALSE);
 }
 
@@ -5693,16 +5676,7 @@ PresShell::StyleRuleRemoved(nsIDocument *aDocument,
                             nsIStyleSheet* aStyleSheet,
                             nsIStyleRule* aStyleRule) 
 { 
-  WillCauseReflow();
-  nsresult  rv = mStyleSet->StyleRuleRemoved(mPresContext, aStyleSheet,
-                                             aStyleRule);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-  // XXX For now reconstruct everything
-  return ReconstructFrames();
+  return ReconstructStyleData(PR_FALSE);
 }
 
 NS_IMETHODIMP
@@ -5796,7 +5770,7 @@ PresShell::BidiStyleChangeReflow()
   nsIFrame* rootFrame;
   mFrameManager->GetRootFrame(&rootFrame);
   if (rootFrame) {
-    mStyleSet->ClearStyleData(mPresContext, nsnull);
+    mStyleSet->ClearStyleData(mPresContext);
     ReconstructFrames();
   }
   return NS_OK;
diff --git a/mozilla/layout/base/public/nsIStyleFrameConstruction.h b/mozilla/layout/base/public/nsIStyleFrameConstruction.h
index 2bc330c6b8b..bdc1c84e3c9 100644
--- a/mozilla/layout/base/public/nsIStyleFrameConstruction.h
+++ b/mozilla/layout/base/public/nsIStyleFrameConstruction.h
@@ -233,61 +233,6 @@ public:
                               nsChangeHint aHint) = 0;
 
 
-  /////////////// Style change notifications ////////////////// 
-
-  /**
-   * A StyleRule has just been modified within a style sheet.
-   *
-   * @param aDocument The document being observed
-   * @param aStyleSheet the StyleSheet that contians the rule
-   * @param aStyleRule  the rule that was modified
-   * @param aHint       some possible info about the nature of the change.
-   *                    see nsStyleConsts for hint values
-   *
-   * @return  NS_OK
-   * @see     nsIDocumentObserver
-   */
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint) = 0; // See nsStyleConsts fot hint values
-
-  /**
-   * A StyleRule has just been added to a style sheet.
-   * This method is called automatically when the rule gets
-   * added to the sheet. The style sheet passes this
-   * notification to the document. The notification is passed on 
-   * to all of the document observers.
-   *
-   * @param aDocument The document being observed
-   * @param aStyleSheet the StyleSheet that has been modified
-   * @param aStyleRule the rule that was added
-   *
-   * @return  NS_OK
-   * @see     nsIDocumentObserver
-   */
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule) = 0;
-
-  /**
-   * A StyleRule has just been removed from a style sheet.
-   * This method is called automatically when the rule gets
-   * removed from the sheet. The style sheet passes this
-   * notification to the document. The notification is passed on 
-   * to all of the document observers.
-   *
-   * @param aDocument The document being observed
-   * @param aStyleSheet the StyleSheet that has been modified
-   * @param aStyleRule the rule that was removed
-   *
-   * @return  NS_OK
-   * @see     nsIDocumentObserver
-   */
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule) = 0;
-
   /**
    * Method that actually handles style changes for effected frames.
    * Note:  this may not need to be a public method.  Use with extreme caution.
diff --git a/mozilla/layout/base/public/nsIStyleSet.h b/mozilla/layout/base/public/nsIStyleSet.h
index 5a4025ad5c1..e237934b263 100644
--- a/mozilla/layout/base/public/nsIStyleSet.h
+++ b/mozilla/layout/base/public/nsIStyleSet.h
@@ -131,13 +131,8 @@ public:
 
   virtual nsresult GetStyleFrameConstruction(nsIStyleFrameConstruction** aResult) = 0;
 
-  // ClearCachedStyleData is used to invalidate portions of both the style context tree
-  // and rule tree without destroying the actual nodes in the two trees.  |aRule| provides
-  // a hint as to which rule has changed, and all subtree data pruning will occur rooted
-  // only on style contexts and rule nodes that use that rule.  If the rule is null, then
-  // it is assumed that both trees are to be entirely wiped.
-  //
-  virtual nsresult ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule) = 0;
+  // Clear all style data cached in the style context tree and rule tree.
+  virtual nsresult ClearStyleData(nsIPresContext* aPresContext) = 0;
 
   // enable / disable the Quirk style sheet: 
   // returns NS_FAILURE if none is found, otherwise NS_OK
@@ -253,18 +248,6 @@ public:
                               PRInt32 aModType, 
                               nsChangeHint aHint) = 0;
 
-  // Style change notifications
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint) = 0;
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule) = 0;
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule) = 0;
-
   // Notification that we were unable to render a replaced element.
   // Called when the replaced element can not be rendered, and we should
   // instead render the element's contents.
diff --git a/mozilla/layout/base/src/nsPresContext.cpp b/mozilla/layout/base/src/nsPresContext.cpp
index 0579fda8ab8..e49206ef765 100644
--- a/mozilla/layout/base/src/nsPresContext.cpp
+++ b/mozilla/layout/base/src/nsPresContext.cpp
@@ -576,7 +576,7 @@ nsPresContext::ClearStyleDataAndReflow()
     // Clear out all our style data.
     nsCOMPtr<nsIStyleSet> set;
     mShell->GetStyleSet(getter_AddRefs(set));
-    set->ClearStyleData(this, nsnull);
+    set->ClearStyleData(this);
 
     // Force a reflow of the root frame
     // XXX We really should only do a reflow if a preference that affects
diff --git a/mozilla/layout/html/base/src/nsPresShell.cpp b/mozilla/layout/html/base/src/nsPresShell.cpp
index ed8be251411..0d99dec0e0f 100644
--- a/mozilla/layout/html/base/src/nsPresShell.cpp
+++ b/mozilla/layout/html/base/src/nsPresShell.cpp
@@ -5657,15 +5657,10 @@ PresShell::StyleSheetApplicableStateChanged(nsIDocument *aDocument,
 NS_IMETHODIMP
 PresShell::StyleRuleChanged(nsIDocument *aDocument,
                             nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule,
-                            nsChangeHint aHint) 
+                            nsIStyleRule* aOldStyleRule,
+                            nsIStyleRule* aNewStyleRule)
 {
-  WillCauseReflow();
-  nsresult  rv = mStyleSet->StyleRuleChanged(mPresContext, aStyleSheet,
-                                             aStyleRule, aHint);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  return rv;
+  return ReconstructStyleData(PR_FALSE);
 }
 
 NS_IMETHODIMP
@@ -5673,18 +5668,6 @@ PresShell::StyleRuleAdded(nsIDocument *aDocument,
                           nsIStyleSheet* aStyleSheet,
                           nsIStyleRule* aStyleRule) 
 { 
-  WillCauseReflow();
-  nsresult rv = mStyleSet->StyleRuleAdded(mPresContext, aStyleSheet,
-                                          aStyleRule);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-
-  // We don't need to rebuild the
-  // rule tree, since no rule nodes have been rendered invalid by the
-  // addition of new rule content.  
   return ReconstructStyleData(PR_FALSE);
 }
 
@@ -5693,16 +5676,7 @@ PresShell::StyleRuleRemoved(nsIDocument *aDocument,
                             nsIStyleSheet* aStyleSheet,
                             nsIStyleRule* aStyleRule) 
 { 
-  WillCauseReflow();
-  nsresult  rv = mStyleSet->StyleRuleRemoved(mPresContext, aStyleSheet,
-                                             aStyleRule);
-  VERIFY_STYLE_TREE;
-  DidCauseReflow();
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-  // XXX For now reconstruct everything
-  return ReconstructFrames();
+  return ReconstructStyleData(PR_FALSE);
 }
 
 NS_IMETHODIMP
@@ -5796,7 +5770,7 @@ PresShell::BidiStyleChangeReflow()
   nsIFrame* rootFrame;
   mFrameManager->GetRootFrame(&rootFrame);
   if (rootFrame) {
-    mStyleSet->ClearStyleData(mPresContext, nsnull);
+    mStyleSet->ClearStyleData(mPresContext);
     ReconstructFrames();
   }
   return NS_OK;
diff --git a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
index 4c283a2f3b7..c7dcf639adc 100644
--- a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
@@ -10553,78 +10553,6 @@ nsCSSFrameConstructor::AttributeChanged(nsIPresContext* aPresContext,
   return result;
 }
 
-  // Style change notifications
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleChanged(nsIPresContext* aPresContext,
-                                        nsIStyleSheet* aStyleSheet,
-                                        nsIStyleRule* aStyleRule,
-                                        nsChangeHint aHint)
-{
-  nsresult result = NS_OK;
-  nsCOMPtr<nsIPresShell> shell;
-  aPresContext->GetShell(getter_AddRefs(shell));
-  nsIFrame* frame;
-  shell->GetRootFrame(&frame);
-
-  if (!frame) {
-    return NS_OK;
-  }
-
-  PRBool reframe = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                             | nsChangeHint_Unknown)) != 0;
-  PRBool restyle = (aHint & ~(nsChangeHint_AttrChange)) != 0;
-  // TBD: add "review" to update view?
-
-  if (restyle) {
-    nsCOMPtr<nsIStyleSet> set;
-    shell->GetStyleSet(getter_AddRefs(set));
-    set->ClearStyleData(aPresContext, aStyleRule);
-  }
-
-  if (reframe) {
-    result = ReconstructDocElementHierarchy(aPresContext);
-  }
-  else {
-    PRBool reflow = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                              | nsChangeHint_ReflowFrame | nsChangeHint_Unknown)) != 0;
-    PRBool renderOrSync = (aHint & (nsChangeHint_ReconstructDoc | nsChangeHint_ReconstructFrame
-                                    | nsChangeHint_ReflowFrame | nsChangeHint_RepaintFrame
-                                    | nsChangeHint_Unknown | nsChangeHint_SyncFrameView)) != 0;
-
-    // XXX hack, skip the root and scrolling frames
-    frame->FirstChild(aPresContext, nsnull, &frame);
-    frame->FirstChild(aPresContext, nsnull, &frame);
-    if (reflow) {
-      StyleChangeReflow(aPresContext, frame, nsnull);
-    }
-    if (renderOrSync) {
-      ApplyRenderingChangeToTree(aPresContext, frame, nsnull, aHint);
-    }
-  }
-
-  return result;
-}
-
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleAdded(nsIPresContext* aPresContext,
-                                      nsIStyleSheet* aStyleSheet,
-                                      nsIStyleRule* aStyleRule)
-{
-  // XXX TBI: should query rule for impact and do minimal work
-  ReconstructDocElementHierarchy(aPresContext);
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-nsCSSFrameConstructor::StyleRuleRemoved(nsIPresContext* aPresContext,
-                                        nsIStyleSheet* aStyleSheet,
-                                        nsIStyleRule* aStyleRule)
-{
-  // XXX TBI: should query rule for impact and do minimal work
-  ReconstructDocElementHierarchy(aPresContext);
-  return NS_OK;
-}
-
 //STATIC
 void nsCSSFrameConstructor::GetAlternateTextFor(nsIContent* aContent,
                                                 nsIAtom*    aTag,  // content object's tag
diff --git a/mozilla/layout/html/style/src/nsCSSFrameConstructor.h b/mozilla/layout/html/style/src/nsCSSFrameConstructor.h
index ef3c7aa26c2..eedc0488573 100644
--- a/mozilla/layout/html/style/src/nsCSSFrameConstructor.h
+++ b/mozilla/layout/html/style/src/nsCSSFrameConstructor.h
@@ -141,20 +141,6 @@ public:
                               PRInt32         aModType, 
                               nsChangeHint    aHint);
 
-  // Style change notifications
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet*  aStyleSheet,
-                              nsIStyleRule*   aStyleRule,
-                              nsChangeHint    aHint);
-
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet*  aStyleSheet,
-                            nsIStyleRule*   aStyleRule);
-
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet*  aStyleSheet,
-                              nsIStyleRule*   aStyleRule);
-
   NS_IMETHOD ProcessRestyledFrames(nsStyleChangeList& aRestyleArray, 
                                    nsIPresContext*    aPresContext);
 
diff --git a/mozilla/layout/style/nsCSSParser.cpp b/mozilla/layout/style/nsCSSParser.cpp
index b248ffea8a2..e52cb771735 100644
--- a/mozilla/layout/style/nsCSSParser.cpp
+++ b/mozilla/layout/style/nsCSSParser.cpp
@@ -640,12 +640,11 @@ CSSParserImpl::ParseStyleAttribute(const nsAString& aAttributeValue,
   if (declaration) {
     // Create a style rule for the delcaration
     nsICSSStyleRule* rule = nsnull;
-    rv = NS_NewCSSStyleRule(&rule, nsnull);
+    rv = NS_NewCSSStyleRule(&rule, nsnull, declaration);
     if (NS_FAILED(rv)) {
       declaration->RuleAbort();
       return rv;
     }
-    rule->SetDeclaration(declaration);
     *aResult = rule;
   }
   else {
@@ -1473,14 +1472,13 @@ PRBool CSSParserImpl::ParseRuleSet(PRInt32& aErrorCode, RuleAppendFunc aAppendFu
   // Translate the selector list and declaration block into style data
 
   nsCOMPtr<nsICSSStyleRule> rule;
-  NS_NewCSSStyleRule(getter_AddRefs(rule), slist);
+  NS_NewCSSStyleRule(getter_AddRefs(rule), slist, declaration);
   if (!rule) {
     aErrorCode = NS_ERROR_OUT_OF_MEMORY;
     delete slist;
     return PR_FALSE;
   }
   rule->SetLineNumber(linenum);
-  rule->SetDeclaration(declaration);
   (*aAppendFunc)(rule, aData);
 
   return PR_TRUE;
diff --git a/mozilla/layout/style/nsCSSRules.cpp b/mozilla/layout/style/nsCSSRules.cpp
index aed43a7e994..a70066583fe 100644
--- a/mozilla/layout/style/nsCSSRules.cpp
+++ b/mozilla/layout/style/nsCSSRules.cpp
@@ -662,6 +662,7 @@ public:
   NS_IMETHOD  EnumerateRulesForwards(nsISupportsArrayEnumFunc aFunc, void * aData) const;
   NS_IMETHOD  DeleteStyleRuleAt(PRUint32 aIndex);
   NS_IMETHOD  InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules);
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule *aOld, nsICSSRule *aNew);
   
   // nsIDOMCSSRule interface
   NS_DECL_NSIDOMCSSRULE
@@ -872,6 +873,8 @@ CSSMediaRuleImpl::AppendStyleRule(nsICSSRule* aRule)
     aRule->SetStyleSheet(mSheet);
     aRule->SetParentRule(this);
     if (mSheet) {
+      // XXXldb Shouldn't we be using |WillDirty| and |DidDirty| (and
+      // shouldn't |SetModified| be removed?
       mSheet->SetModified(PR_TRUE);
     }
   }
@@ -952,6 +955,18 @@ CSSMediaRuleImpl::InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSMediaRuleImpl::ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  PRInt32 index = mRules->IndexOf(aOld);
+  NS_ENSURE_TRUE(index != -1, NS_ERROR_UNEXPECTED);
+  mRules->ReplaceElementAt(aNew, index);
+  aNew->SetStyleSheet(mSheet);
+  aNew->SetParentRule(this);
+  aOld->SetStyleSheet(nsnull);
+  aOld->SetParentRule(nsnull);
+  return NS_OK;
+}
 
 nsresult
 NS_NewCSSMediaRule(nsICSSMediaRule** aInstancePtrResult)
diff --git a/mozilla/layout/style/nsCSSStyleRule.cpp b/mozilla/layout/style/nsCSSStyleRule.cpp
index e72cabd41df..b428220ca60 100644
--- a/mozilla/layout/style/nsCSSStyleRule.cpp
+++ b/mozilla/layout/style/nsCSSStyleRule.cpp
@@ -854,7 +854,7 @@ CSSImportantRule::List(FILE* out, PRInt32 aIndent) const
 }
 #endif
 
-// -- nsDOMStyleRuleDeclaration -------------------------------
+// -- DOMCSSDeclarationImpl -------------------------------
 
 class DOMCSSDeclarationImpl : public nsDOMCSSDeclaration
 {
@@ -862,24 +862,14 @@ public:
   DOMCSSDeclarationImpl(nsICSSStyleRule *aRule);
   ~DOMCSSDeclarationImpl(void);
 
-  NS_IMETHOD RemoveProperty(const nsAString& aPropertyName, 
-                            nsAString& aReturn);
-
   virtual void DropReference(void);
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate);
-  virtual nsresult GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
-                                            nsICSSStyleSheet** aSheet,
-                                            nsIDocument** aDocument,
-                                            nsIURI** aURI,
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aURI,
                                             nsICSSLoader** aCSSLoader,
                                             nsICSSParser** aCSSParser);
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue);
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl);
   virtual nsresult GetParent(nsISupports **aParent);
+  virtual nsresult DeclarationChanged();
 
 protected:
   nsICSSStyleRule *mRule;
@@ -901,55 +891,6 @@ DOMCSSDeclarationImpl::~DOMCSSDeclarationImpl(void)
   MOZ_COUNT_DTOR(DOMCSSDeclarationImpl);
 }
 
-NS_IMETHODIMP
-DOMCSSDeclarationImpl::RemoveProperty(const nsAString& aPropertyName, 
-                                      nsAString& aReturn)
-{
-  aReturn.Truncate();
-
-  nsCSSDeclaration* decl;
-  nsresult rv = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (NS_SUCCEEDED(rv) && decl) {
-    nsCOMPtr<nsICSSStyleSheet> cssSheet;
-    nsCOMPtr<nsIDocument> owningDoc;
-    if (mRule) {
-      nsCOMPtr<nsIStyleSheet> sheet;
-      mRule->GetStyleSheet(*getter_AddRefs(sheet));
-      cssSheet = do_QueryInterface(sheet);
-      if (sheet) {
-        sheet->GetOwningDocument(*getter_AddRefs(owningDoc));
-      }
-    }
-    if (owningDoc) {
-      owningDoc->BeginUpdate();
-    }
-    nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
-
-    decl->GetValue(prop, aReturn);
-
-    rv = decl->RemoveProperty(prop);
-
-    if (NS_SUCCEEDED(rv)) {
-      if (cssSheet) {
-        cssSheet->SetModified(PR_TRUE);
-      }
-      if (owningDoc) {
-        owningDoc->StyleRuleChanged(cssSheet, mRule, nsCSSProps::kHintTable[prop]);
-      }
-    } else {
-      // If we tried to remove an invalid property or a property that wasn't 
-      //  set we simply return success and an empty string
-      rv = NS_OK;
-    }
-    if (owningDoc) {
-      owningDoc->EndUpdate();
-    }
-  }
-
-  return rv;
-}
-
 void 
 DOMCSSDeclarationImpl::DropReference(void)
 {
@@ -972,38 +913,34 @@ DOMCSSDeclarationImpl::GetCSSDeclaration(nsCSSDeclaration **aDecl,
 
 /*
  * This is a utility function.  It will only fail if it can't get a
- * parser.  This means it can return NS_OK without all of aSheet,
- *  aDocument, aURI, aCSSLoader being initialized
+ * parser.  This means it can return NS_OK without aURI or aCSSLoader
+ * being initialized.
  */
 nsresult
-DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
-                                                nsICSSStyleSheet** aSheet,
-                                                nsIDocument** aDocument,
-                                                nsIURI** aURI,
+DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsIURI** aURI,
                                                 nsICSSLoader** aCSSLoader,
                                                 nsICSSParser** aCSSParser)
 {
   // null out the out params since some of them may not get initialized below
-  *aSheet = nsnull;
-  *aDocument = nsnull;
   *aURI = nsnull;
   *aCSSLoader = nsnull;
   *aCSSParser = nsnull;
   nsresult result;
   nsCOMPtr<nsIStyleSheet> sheet;
-  if (aRule) {
-    aRule->GetStyleSheet(*getter_AddRefs(sheet));
+  if (mRule) {
+    mRule->GetStyleSheet(*getter_AddRefs(sheet));
     if (sheet) {
-      CallQueryInterface(sheet, aSheet);
-      sheet->GetOwningDocument(*aDocument);
       sheet->GetURL(*aURI);
+      nsCOMPtr<nsIDocument> document;
+      sheet->GetOwningDocument(*getter_AddRefs(document));
+      nsCOMPtr<nsIHTMLContentContainer> htmlContainer =
+        do_QueryInterface(document);
+      if (htmlContainer) {
+        htmlContainer->GetCSSLoader(*aCSSLoader);
+        NS_ASSERTION(*aCSSLoader, "Document with no CSS loader!");
+      }
     }
   }
-  nsCOMPtr<nsIHTMLContentContainer> htmlContainer(do_QueryInterface(*aDocument));
-  if (htmlContainer) {
-    htmlContainer->GetCSSLoader(*aCSSLoader);
-  }
-  NS_ASSERTION(*aCSSLoader || !*aDocument, "Document with no CSS loader!");
   if (*aCSSLoader) {
     result = (*aCSSLoader)->GetParserFor(nsnull, aCSSParser);
   } else {
@@ -1013,99 +950,6 @@ DOMCSSDeclarationImpl::GetCSSParsingEnvironment(nsICSSStyleRule* aRule,
   return result;
 }
 
-nsresult
-DOMCSSDeclarationImpl::ParsePropertyValue(const nsAString& aPropName,
-                                          const nsAString& aPropValue)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-  if (!decl) {
-    return result;
-  }
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-  nsCOMPtr<nsICSSStyleSheet> cssSheet;
-  nsCOMPtr<nsIDocument> owningDoc;
-  result = GetCSSParsingEnvironment(mRule,
-                                    getter_AddRefs(cssSheet),
-                                    getter_AddRefs(owningDoc),
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-
-  if (NS_FAILED(result)) {
-    return result;
-  }
-  
-  nsChangeHint hint;
-  if (owningDoc) {
-    owningDoc->BeginUpdate();
-  }
-  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl, &hint);
-  if (NS_SUCCEEDED(result)) {
-    if (cssSheet) {
-      cssSheet->SetModified(PR_TRUE);
-    }
-    if (owningDoc) {
-      owningDoc->StyleRuleChanged(cssSheet, mRule, hint);
-      owningDoc->EndUpdate();
-    }
-  }
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
-nsresult 
-DOMCSSDeclarationImpl::ParseDeclaration(const nsAString& aDecl,
-                                        PRBool aParseOnlyOneDecl,
-                                        PRBool aClearOldDecl)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (decl) {
-    nsCOMPtr<nsICSSLoader> cssLoader;
-    nsCOMPtr<nsICSSParser> cssParser;
-    nsCOMPtr<nsIURI> baseURI;
-    nsCOMPtr<nsICSSStyleSheet> cssSheet;
-    nsCOMPtr<nsIDocument> owningDoc;
-
-    result = GetCSSParsingEnvironment(mRule,
-                                      getter_AddRefs(cssSheet),
-                                      getter_AddRefs(owningDoc),
-                                      getter_AddRefs(baseURI),
-                                      getter_AddRefs(cssLoader),
-                                      getter_AddRefs(cssParser));
-
-    if (NS_SUCCEEDED(result)) {
-      nsChangeHint hint;
-      result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
-                                                    aParseOnlyOneDecl, &hint,
-                                                    aClearOldDecl);
-
-      if (NS_SUCCEEDED(result)) {
-        if (cssSheet) {
-          cssSheet->SetModified(PR_TRUE);
-        }
-        if (owningDoc) {
-          owningDoc->StyleRuleChanged(cssSheet, mRule, hint);
-        }
-      }
-      if (cssLoader) {
-        cssLoader->RecycleParser(cssParser);
-      }
-    }
-  }
-
-  return result;
-}
-
-
-
 nsresult 
 DOMCSSDeclarationImpl::GetParent(nsISupports **aParent)
 {
@@ -1120,6 +964,37 @@ DOMCSSDeclarationImpl::GetParent(nsISupports **aParent)
   return NS_OK;
 }
 
+nsresult
+DOMCSSDeclarationImpl::DeclarationChanged()
+{
+  NS_PRECONDITION(mRule,
+         "can only be called when |GetCSSDeclaration| returned a declaration");
+
+  nsCOMPtr<nsIDocument> owningDoc;
+  nsCOMPtr<nsIStyleSheet> sheet;
+  mRule->GetStyleSheet(*getter_AddRefs(sheet));
+  if (sheet) {
+    sheet->GetOwningDocument(*getter_AddRefs(owningDoc));
+  }
+
+  if (owningDoc) {
+    // XXXldb Do we need to bother with this?  We're now doing it in
+    // more places than we used to, but it probably doesn't matter...
+    owningDoc->BeginUpdate();
+  }
+
+  nsCOMPtr<nsICSSStyleRule> oldRule = mRule;
+  mRule = oldRule->DeclarationChanged(PR_TRUE).get();
+  nsrefcnt cnt = mRule->Release();
+  NS_ASSERTION(cnt != 0, "container didn't take ownership");
+
+  if (owningDoc) {
+    owningDoc->StyleRuleChanged(sheet, oldRule, mRule);
+    owningDoc->EndUpdate();
+  }
+  return NS_OK;
+}
+
 // -- nsCSSStyleRule -------------------------------
 
 class CSSStyleRuleImpl : public nsCSSRule,
@@ -1127,8 +1002,15 @@ class CSSStyleRuleImpl : public nsCSSRule,
                          public nsIDOMCSSStyleRule
 {
 public:
-  CSSStyleRuleImpl(nsCSSSelectorList* aSelector);
+  CSSStyleRuleImpl(nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration *aDeclaration);
+private:
+  // for |Clone|
   CSSStyleRuleImpl(const CSSStyleRuleImpl& aCopy); 
+  // for |DeclarationChanged|
+  CSSStyleRuleImpl(CSSStyleRuleImpl& aCopy,
+                   nsCSSDeclaration *aDeclaration); 
+public:
 
   NS_DECL_ISUPPORTS_INHERITED
 
@@ -1138,7 +1020,6 @@ public:
   virtual void SetLineNumber(PRUint32 aLineNumber);
 
   virtual nsCSSDeclaration* GetDeclaration(void) const;
-  virtual void SetDeclaration(nsCSSDeclaration* aDeclaration);
 
   virtual already_AddRefed<nsIStyleRule> GetImportantRule(void);
 
@@ -1153,6 +1034,9 @@ public:
   NS_IMETHOD GetType(PRInt32& aType) const;
   NS_IMETHOD Clone(nsICSSRule*& aClone) const;
 
+  virtual already_AddRefed<nsICSSStyleRule>
+    DeclarationChanged(PRBool aHandleContainer);
+
   // The new mapping function.
   NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData);
 
@@ -1181,30 +1065,50 @@ protected:
   PRUint32                mLineNumber;
 };
 
-CSSStyleRuleImpl::CSSStyleRuleImpl(nsCSSSelectorList* aSelector)
+CSSStyleRuleImpl::CSSStyleRuleImpl(nsCSSSelectorList* aSelector,
+                                   nsCSSDeclaration* aDeclaration)
   : nsCSSRule(),
-    mSelector(aSelector), mDeclaration(nsnull), 
+    mSelector(aSelector),
+    mDeclaration(aDeclaration), 
     mImportantRule(nsnull),
     mDOMDeclaration(nsnull)
 {
+  if (mDeclaration)
+    mDeclaration->AddRef();
 }
 
+// for |Clone|
 CSSStyleRuleImpl::CSSStyleRuleImpl(const CSSStyleRuleImpl& aCopy)
   : nsCSSRule(aCopy),
     mSelector(aCopy.mSelector ? aCopy.mSelector->Clone() : nsnull),
-    mDeclaration(nsnull),
+    mDeclaration(aCopy.mDeclaration ? aCopy.mDeclaration->Clone() : nsnull),
     mImportantRule(nsnull),
     mDOMDeclaration(nsnull)
 {
-  if (aCopy.mDeclaration) {
-    mDeclaration = aCopy.mDeclaration->Clone();
-    if (nsnull != mDeclaration) {
-      mDeclaration->AddRef();
-    }
-  }
+  if (mDeclaration)
+    mDeclaration->AddRef();
   // rest is constructed lazily on existing data
 }
 
+// for |DeclarationChanged|
+CSSStyleRuleImpl::CSSStyleRuleImpl(CSSStyleRuleImpl& aCopy,
+                                   nsCSSDeclaration* aDeclaration)
+  : nsCSSRule(aCopy),
+    mSelector(aCopy.mSelector),
+    mDeclaration(aDeclaration),
+    mImportantRule(nsnull),
+    mDOMDeclaration(aCopy.mDOMDeclaration)
+{
+  // The DOM declaration is replacing |aCopy| with |this|, so transfer
+  // the reverse pointer as well.
+  aCopy.mDOMDeclaration = nsnull;
+
+  // Transfer ownership of selector and declaration:
+  NS_ASSERTION(aDeclaration == aCopy.mDeclaration, "declaration mismatch");
+  aCopy.mSelector = nsnull;
+  aCopy.mDeclaration = nsnull;
+}
+
 
 CSSStyleRuleImpl::~CSSStyleRuleImpl(void)
 {
@@ -1259,20 +1163,7 @@ void CSSStyleRuleImpl::SetLineNumber(PRUint32 aLineNumber)
 
 nsCSSDeclaration* CSSStyleRuleImpl::GetDeclaration(void) const
 {
-  nsCSSDeclaration* result = mDeclaration;
-  return result;
-}
-
-void CSSStyleRuleImpl::SetDeclaration(nsCSSDeclaration* aDeclaration)
-{
-  if (mDeclaration != aDeclaration) {
-    NS_IF_RELEASE(mImportantRule); 
-    if (nsnull != mDeclaration) {
-      mDeclaration->Release();
-    }
-    mDeclaration = aDeclaration;
-    mDeclaration->AddRef();
-  }
+  return mDeclaration;
 }
 
 already_AddRefed<nsIStyleRule> CSSStyleRuleImpl::GetImportantRule(void)
@@ -1326,11 +1217,32 @@ NS_IMETHODIMP
 CSSStyleRuleImpl::Clone(nsICSSRule*& aClone) const
 {
   CSSStyleRuleImpl* clone = new CSSStyleRuleImpl(*this);
-  if (clone) {
-    return CallQueryInterface(clone, &aClone);
+  if (!clone) {
+    aClone = nsnull;
+    return NS_ERROR_OUT_OF_MEMORY;
   }
-  aClone = nsnull;
-  return NS_ERROR_OUT_OF_MEMORY;
+  return CallQueryInterface(clone, &aClone);
+}
+
+/* virtual */ already_AddRefed<nsICSSStyleRule>
+CSSStyleRuleImpl::DeclarationChanged(PRBool aHandleContainer)
+{
+  CSSStyleRuleImpl* clone = new CSSStyleRuleImpl(*this, mDeclaration);
+  if (!clone) {
+    return nsnull;
+  }
+
+  NS_ADDREF(clone); // for return
+
+  if (aHandleContainer) {
+    if (mParentRule) {
+      mSheet->ReplaceRuleInGroup(mParentRule, this, clone);
+    } else {
+      mSheet->ReplaceStyleRule(this, clone);
+    }
+  }
+
+  return clone;
 }
 
 NS_IMETHODIMP
@@ -1457,13 +1369,10 @@ CSSStyleRuleImpl::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
 
 nsresult
 NS_NewCSSStyleRule(nsICSSStyleRule** aInstancePtrResult,
-                   nsCSSSelectorList* aSelector)
+                   nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration* aDeclaration)
 {
-  if (aInstancePtrResult == nsnull) {
-    return NS_ERROR_NULL_POINTER;
-  }
-
-  CSSStyleRuleImpl *it = new CSSStyleRuleImpl(aSelector);
+  CSSStyleRuleImpl *it = new CSSStyleRuleImpl(aSelector, aDeclaration);
   if (!it) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
diff --git a/mozilla/layout/style/nsCSSStyleSheet.cpp b/mozilla/layout/style/nsCSSStyleSheet.cpp
index d93fa334b6b..9fc2ff1945c 100644
--- a/mozilla/layout/style/nsCSSStyleSheet.cpp
+++ b/mozilla/layout/style/nsCSSStyleSheet.cpp
@@ -819,6 +819,7 @@ public:
   NS_IMETHOD ClearMedia(void);
   NS_IMETHOD DeleteRuleFromGroup(nsICSSGroupRule* aGroup, PRUint32 aIndex);
   NS_IMETHOD InsertRuleIntoGroup(const nsAString& aRule, nsICSSGroupRule* aGroup, PRUint32 aIndex, PRUint32* _retval);
+  NS_IMETHOD ReplaceRuleInGroup(nsICSSGroupRule* aGroup, nsICSSRule* aOld, nsICSSRule* aNew);
   
   NS_IMETHOD GetApplicable(PRBool& aApplicable) const;
   
@@ -847,6 +848,7 @@ public:
   // XXX do these belong here or are they generic?
   NS_IMETHOD PrependStyleRule(nsICSSRule* aRule);
   NS_IMETHOD AppendStyleRule(nsICSSRule* aRule);
+  NS_IMETHOD ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew);
 
   NS_IMETHOD  StyleRuleCount(PRInt32& aCount) const;
   NS_IMETHOD  GetStyleRuleAt(PRInt32 aIndex, nsICSSRule*& aRule) const;
@@ -1354,7 +1356,8 @@ DOMMediaListImpl::EndMediaChange(void)
     mStyleSheet->DidDirty();
     rv = mStyleSheet->GetOwningDocument(*getter_AddRefs(doc));
     NS_ENSURE_SUCCESS(rv, rv);
-    rv = doc->StyleRuleChanged(mStyleSheet, nsnull, NS_STYLE_HINT_RECONSTRUCT_ALL);
+    // XXXldb Pass something meaningful?
+    rv = doc->StyleRuleChanged(mStyleSheet, nsnull, nsnull);
     NS_ENSURE_SUCCESS(rv, rv);
     rv = doc->EndUpdate();
     NS_ENSURE_SUCCESS(rv, rv);
@@ -2159,6 +2162,32 @@ CSSStyleSheetImpl::AppendStyleRule(nsICSSRule* aRule)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSStyleSheetImpl::ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  NS_PRECONDITION(mInner->mOrderedRules, "can't have old rule");
+  NS_PRECONDITION(mInner && mInner->mComplete,
+                  "No replacing in an incomplete sheet!");
+
+  if (NS_SUCCEEDED(WillDirty())) {
+    PRInt32 index = mInner->mOrderedRules->IndexOf(aOld);
+    NS_ENSURE_TRUE(index != -1, NS_ERROR_UNEXPECTED);
+    mInner->mOrderedRules->ReplaceElementAt(aNew, index);
+
+    aNew->SetStyleSheet(this);
+    aOld->SetStyleSheet(nsnull);
+    DidDirty();
+#ifdef DEBUG
+    PRInt32 type = nsICSSRule::UNKNOWN_RULE;
+    aNew->GetType(type);
+    NS_ASSERTION(nsICSSRule::NAMESPACE_RULE != type, "not yet implemented");
+    aOld->GetType(type);
+    NS_ASSERTION(nsICSSRule::NAMESPACE_RULE != type, "not yet implemented");
+#endif
+  }
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 CSSStyleSheetImpl::StyleRuleCount(PRInt32& aCount) const
 {
@@ -2981,6 +3010,29 @@ CSSStyleSheetImpl::InsertRuleIntoGroup(const nsAString & aRule, nsICSSGroupRule*
   return NS_OK;
 }
 
+NS_IMETHODIMP
+CSSStyleSheetImpl::ReplaceRuleInGroup(nsICSSGroupRule* aGroup,
+                                      nsICSSRule* aOld, nsICSSRule* aNew)
+{
+  nsresult result;
+  NS_PRECONDITION(mInner && mInner->mComplete,
+                  "No replacing in an incomplete sheet!");
+#ifdef DEBUG
+  {
+    nsCOMPtr<nsIDOMCSSRule> domGroup(do_QueryInterface(aGroup));
+    nsCOMPtr<nsIDOMCSSStyleSheet> groupSheet;
+    domGroup->GetParentStyleSheet(getter_AddRefs(groupSheet));
+    NS_ASSERTION(this == groupSheet, "group doesn't belong to this sheet");
+  }
+#endif
+  result = WillDirty();
+  NS_ENSURE_SUCCESS(result, result);
+
+  result = aGroup->ReplaceStyleRule(aOld, aNew);
+  DidDirty();
+  return result;
+}
+
 // nsICSSLoaderObserver implementation
 NS_IMETHODIMP
 CSSStyleSheetImpl::StyleSheetLoaded(nsICSSStyleSheet*aSheet, PRBool aNotify)
diff --git a/mozilla/layout/style/nsDOMCSSAttrDeclaration.cpp b/mozilla/layout/style/nsDOMCSSAttrDeclaration.cpp
index ddadc3b3ea1..ca1e51a4d7c 100644
--- a/mozilla/layout/style/nsDOMCSSAttrDeclaration.cpp
+++ b/mozilla/layout/style/nsDOMCSSAttrDeclaration.cpp
@@ -68,35 +68,6 @@ nsDOMCSSAttributeDeclaration::~nsDOMCSSAttributeDeclaration()
   MOZ_COUNT_DTOR(nsDOMCSSAttributeDeclaration);
 }
 
-NS_IMETHODIMP
-nsDOMCSSAttributeDeclaration::RemoveProperty(const nsAString& aPropertyName,
-                                             nsAString& aReturn)
-{
-  aReturn.Truncate();
-
-  nsCSSDeclaration* decl;
-  nsresult rv = GetCSSDeclaration(&decl, PR_FALSE);
-
-  if (NS_SUCCEEDED(rv) && decl) {
-    nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
-
-    decl->GetValue(prop, aReturn);
-
-    rv = decl->RemoveProperty(prop);
-
-    if (NS_SUCCEEDED(rv)) {
-      rv = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-    } else {
-      // RemoveProperty will throw in all sorts of situations -- eg if
-      // the property is a shorthand one.  Do not propagate its return
-      // value to callers.
-      rv = NS_OK;
-    }
-  }
-
-  return rv;
-}
-
 void
 nsDOMCSSAttributeDeclaration::DropReference()
 {
@@ -104,26 +75,25 @@ nsDOMCSSAttributeDeclaration::DropReference()
 }
 
 nsresult
-nsDOMCSSAttributeDeclaration::SetCSSDeclaration(nsCSSDeclaration* aDecl,
-                                                PRBool aNotify,
-                                                PRBool aDeclOwnedByRule)
+nsDOMCSSAttributeDeclaration::DeclarationChanged()
 {
   NS_ASSERTION(mContent, "Must have content node to set the decl!");
-  NS_PRECONDITION(aDecl, "Null decl!");
-    
-  nsCOMPtr<nsICSSStyleRule> cssRule;
-  nsresult rv = NS_NewCSSStyleRule(getter_AddRefs(cssRule), nsnull);
-  if (NS_FAILED(rv)) {
-    if (!aDeclOwnedByRule) {
-      aDecl->RuleAbort();
-    }
-    return rv;
+  nsHTMLValue val;
+  nsresult rv = mContent->GetHTMLAttribute(nsHTMLAtoms::style, val);
+  NS_ASSERTION(rv == NS_CONTENT_ATTR_HAS_VALUE &&
+               eHTMLUnit_ISupports == val.GetUnit(),
+               "content must have rule");
+  nsCOMPtr<nsICSSStyleRule> oldRule =
+    do_QueryInterface(nsCOMPtr<nsISupports>(val.GetISupportsValue()));
+
+  nsCOMPtr<nsICSSStyleRule> newRule = oldRule->DeclarationChanged(PR_FALSE);
+  if (!newRule) {
+    return NS_ERROR_OUT_OF_MEMORY;
   }
     
-  cssRule->SetDeclaration(aDecl);
   return mContent->SetHTMLAttribute(nsHTMLAtoms::style,
-                                    nsHTMLValue(cssRule),
-                                    aNotify);
+                                    nsHTMLValue(newRule),
+                                    PR_TRUE);
 }
 
 nsresult
@@ -152,7 +122,17 @@ nsDOMCSSAttributeDeclaration::GetCSSDeclaration(nsCSSDeclaration **aDecl,
         decl->RuleAbort();
         return NS_ERROR_OUT_OF_MEMORY;
       }
-      result = SetCSSDeclaration(decl, PR_FALSE, PR_FALSE);
+
+      nsCOMPtr<nsICSSStyleRule> cssRule;
+      result = NS_NewCSSStyleRule(getter_AddRefs(cssRule), nsnull, decl);
+      if (NS_FAILED(result)) {
+        decl->RuleAbort();
+        return result;
+      }
+        
+      result = mContent->SetHTMLAttribute(nsHTMLAtoms::style,
+                                          nsHTMLValue(cssRule),
+                                          PR_FALSE);
       if (NS_SUCCEEDED(result)) {
         *aDecl = decl;
       }
@@ -165,22 +145,21 @@ nsDOMCSSAttributeDeclaration::GetCSSDeclaration(nsCSSDeclaration **aDecl,
 /*
  * This is a utility function.  It will only fail if it can't get a
  * parser.  This means it can return NS_OK without aURI or aCSSLoader
- * being initialized
+ * being initialized.
  */
 nsresult
-nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIContent* aContent,
-                                                       nsIURI** aBaseURI,
+nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIURI** aBaseURI,
                                                        nsICSSLoader** aCSSLoader,
                                                        nsICSSParser** aCSSParser)
 {
-  NS_ASSERTION(aContent, "Something is severely broken -- there should be an nsIContent here!");
+  NS_ASSERTION(mContent, "Something is severely broken -- there should be an nsIContent here!");
   // null out the out params since some of them may not get initialized below
   *aBaseURI = nsnull;
   *aCSSLoader = nsnull;
   *aCSSParser = nsnull;
   
   nsCOMPtr<nsINodeInfo> nodeInfo;
-  nsresult result = aContent->GetNodeInfo(getter_AddRefs(nodeInfo));
+  nsresult result = mContent->GetNodeInfo(getter_AddRefs(nodeInfo));
   if (NS_FAILED(result)) {
     return result;
   }
@@ -214,85 +193,6 @@ nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(nsIContent* aContent,
   return NS_OK;
 }
 
-nsresult
-nsDOMCSSAttributeDeclaration::ParsePropertyValue(const nsAString& aPropName,
-                                                 const nsAString& aPropValue)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (!decl) {
-    return result;
-  }
-  
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-  
-  result = GetCSSParsingEnvironment(mContent,
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-  if (NS_FAILED(result)) {
-    return result;
-  }
-
-  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
-  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl,
-                                    &uselessHint);
-  if (NS_SUCCEEDED(result)) {
-    result = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-  }
-
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
-nsresult
-nsDOMCSSAttributeDeclaration::ParseDeclaration(const nsAString& aDecl,
-                                               PRBool aParseOnlyOneDecl,
-                                               PRBool aClearOldDecl)
-{
-  nsCSSDeclaration* decl;
-  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
-
-  if (!decl) {
-    return result;
-  }
-
-  nsCOMPtr<nsICSSLoader> cssLoader;
-  nsCOMPtr<nsICSSParser> cssParser;
-  nsCOMPtr<nsIURI> baseURI;
-
-  result = GetCSSParsingEnvironment(mContent,
-                                    getter_AddRefs(baseURI),
-                                    getter_AddRefs(cssLoader),
-                                    getter_AddRefs(cssParser));
-
-  if (NS_FAILED(result)) {
-    return result;
-  }
-
-  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
-  result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
-                                                aParseOnlyOneDecl,
-                                                &uselessHint,
-                                                aClearOldDecl);
-  
-  if (NS_SUCCEEDED(result)) {
-    result = SetCSSDeclaration(decl, PR_TRUE, PR_TRUE);
-  }
-
-  if (cssLoader) {
-    cssLoader->RecycleParser(cssParser);
-  }
-
-  return result;
-}
-
 nsresult
 nsDOMCSSAttributeDeclaration::GetParent(nsISupports **aParent)
 {
diff --git a/mozilla/layout/style/nsDOMCSSAttrDeclaration.h b/mozilla/layout/style/nsDOMCSSAttrDeclaration.h
index 1d2abb93c0e..97575e4e098 100644
--- a/mozilla/layout/style/nsDOMCSSAttrDeclaration.h
+++ b/mozilla/layout/style/nsDOMCSSAttrDeclaration.h
@@ -55,28 +55,18 @@ public:
   nsDOMCSSAttributeDeclaration(nsIHTMLContent *aContent);
   ~nsDOMCSSAttributeDeclaration();
 
-  NS_IMETHOD RemoveProperty(const nsAString& aPropertyName,
-                            nsAString& aReturn);
-
   virtual void DropReference();
   // If GetCSSDeclaration returns non-null, then the decl it returns
   // is owned by our current style rule.
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate);
-  virtual nsresult GetCSSParsingEnvironment(nsIContent* aContent,
-                                            nsIURI** aBaseURI,
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aBaseURI,
                                             nsICSSLoader** aCSSLoader,
                                             nsICSSParser** aCSSParser);
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue);
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl);
   virtual nsresult GetParent(nsISupports **aParent);
 
 protected:
-  nsresult SetCSSDeclaration(nsCSSDeclaration* aDecl, PRBool aNotify,
-                             PRBool aDeclOwnedByRule);
+  virtual nsresult DeclarationChanged();
   
   nsIHTMLContent *mContent;
 };
diff --git a/mozilla/layout/style/nsDOMCSSDeclaration.cpp b/mozilla/layout/style/nsDOMCSSDeclaration.cpp
index 7f7f861b7f2..4ccba2920e5 100644
--- a/mozilla/layout/style/nsDOMCSSDeclaration.cpp
+++ b/mozilla/layout/style/nsDOMCSSDeclaration.cpp
@@ -39,6 +39,7 @@
 #include "nsDOMCSSDeclaration.h"
 #include "nsIDOMCSSRule.h"
 #include "nsICSSParser.h"
+#include "nsICSSLoader.h"
 #include "nsIStyleRule.h"
 #include "nsCSSDeclaration.h"
 #include "nsCSSProps.h"
@@ -138,9 +139,10 @@ nsDOMCSSDeclaration::GetLength(PRUint32* aLength)
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
  
-  *aLength = 0;
-  if ((NS_OK == result) && (nsnull != decl)) {
+  if (decl) {
     *aLength = decl->Count();
+  } else {
+    *aLength = 0;
   }
 
   return result;
@@ -182,7 +184,7 @@ nsDOMCSSDeclaration::Item(PRUint32 aIndex, nsAString& aReturn)
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
 
   aReturn.SetLength(0);
-  if ((NS_OK == result) && (nsnull != decl)) {
+  if (decl) {
     result = decl->GetNthProperty(aIndex, aReturn);
   }
 
@@ -197,8 +199,8 @@ nsDOMCSSDeclaration::GetPropertyValue(const nsAString& aPropertyName,
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
 
-  aReturn.SetLength(0);
-  if ((NS_OK == result) && (nsnull != decl)) {
+  aReturn.Truncate();
+  if (decl) {
     result = decl->GetValue(aPropertyName, aReturn);
   }
 
@@ -211,18 +213,11 @@ nsDOMCSSDeclaration::GetPropertyPriority(const nsAString& aPropertyName,
 {
   nsCSSDeclaration *decl;
   nsresult result = GetCSSDeclaration(&decl, PR_FALSE);
-  PRBool isImportant = PR_FALSE;
 
-  if ((NS_OK == result) && (nsnull != decl)) {
-    isImportant = decl->GetValueIsImportant(aPropertyName);
-  }
-
-  if ((NS_OK == result) && isImportant) {
+  aReturn.Truncate();
+  if (decl && decl->GetValueIsImportant(aPropertyName)) {
     aReturn.Assign(NS_LITERAL_STRING("important"));    
   }
-  else {
-    aReturn.SetLength(0);
-  }
 
   return result;
 }
@@ -252,6 +247,112 @@ nsDOMCSSDeclaration::SetProperty(const nsAString& aPropertyName,
                           PR_TRUE, PR_FALSE);
 }
 
+NS_IMETHODIMP
+nsDOMCSSDeclaration::RemoveProperty(const nsAString& aPropertyName,
+                                    nsAString& aReturn)
+{
+  aReturn.Truncate();
+
+  nsCSSDeclaration* decl;
+  nsresult rv = GetCSSDeclaration(&decl, PR_FALSE);
+  if (!decl) {
+    return rv;
+  }
+
+  nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
+
+  decl->GetValue(prop, aReturn);
+
+  rv = decl->RemoveProperty(prop);
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = DeclarationChanged();
+  } else {
+    // RemoveProperty used to throw in all sorts of situations -- e.g.
+    // if the property was a shorthand one.  Do not propagate its return
+    // value to callers.  (XXX or should we propagate it again now?)
+    rv = NS_OK;
+  }
+
+  return rv;
+}
+
+nsresult
+nsDOMCSSDeclaration::ParsePropertyValue(const nsAString& aPropName,
+                                        const nsAString& aPropValue)
+{
+  nsCSSDeclaration* decl;
+  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
+  if (!decl) {
+    return result;
+  }
+  
+  nsCOMPtr<nsICSSLoader> cssLoader;
+  nsCOMPtr<nsICSSParser> cssParser;
+  nsCOMPtr<nsIURI> baseURI;
+  
+  result = GetCSSParsingEnvironment(getter_AddRefs(baseURI),
+                                    getter_AddRefs(cssLoader),
+                                    getter_AddRefs(cssParser));
+  if (NS_FAILED(result)) {
+    return result;
+  }
+
+  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
+  result = cssParser->ParseProperty(aPropName, aPropValue, baseURI, decl,
+                                    &uselessHint);
+  if (NS_SUCCEEDED(result)) {
+    result = DeclarationChanged();
+  }
+
+  if (cssLoader) {
+    cssLoader->RecycleParser(cssParser);
+  }
+
+  return result;
+}
+
+nsresult
+nsDOMCSSDeclaration::ParseDeclaration(const nsAString& aDecl,
+                                      PRBool aParseOnlyOneDecl,
+                                      PRBool aClearOldDecl)
+{
+  nsCSSDeclaration* decl;
+  nsresult result = GetCSSDeclaration(&decl, PR_TRUE);
+  if (!decl) {
+    return result;
+  }
+
+  nsCOMPtr<nsICSSLoader> cssLoader;
+  nsCOMPtr<nsICSSParser> cssParser;
+  nsCOMPtr<nsIURI> baseURI;
+
+  result = GetCSSParsingEnvironment(getter_AddRefs(baseURI),
+                                    getter_AddRefs(cssLoader),
+                                    getter_AddRefs(cssParser));
+
+  if (NS_FAILED(result)) {
+    return result;
+  }
+
+  nsChangeHint uselessHint = NS_STYLE_HINT_NONE;
+  result = cssParser->ParseAndAppendDeclaration(aDecl, baseURI, decl,
+                                                aParseOnlyOneDecl,
+                                                &uselessHint,
+                                                aClearOldDecl);
+  
+  if (NS_SUCCEEDED(result)) {
+    result = DeclarationChanged();
+  }
+
+  if (cssLoader) {
+    cssLoader->RecycleParser(cssParser);
+  }
+
+  return result;
+}
+
+
 //////////////////////////////////////////////////////////////////////////////
 
 CSS2PropertiesTearoff::CSS2PropertiesTearoff(nsISupports *aOuter)
diff --git a/mozilla/layout/style/nsDOMCSSDeclaration.h b/mozilla/layout/style/nsDOMCSSDeclaration.h
index 7f0e19e2a05..9421f67683e 100644
--- a/mozilla/layout/style/nsDOMCSSDeclaration.h
+++ b/mozilla/layout/style/nsDOMCSSDeclaration.h
@@ -47,6 +47,7 @@
 
 class nsCSSDeclaration;
 class nsICSSParser;
+class nsICSSLoader;
 class nsIURI;
 
 class nsDOMCSSDeclaration : public nsIDOMCSSStyleDeclaration
@@ -56,35 +57,28 @@ public:
 
   NS_DECL_ISUPPORTS
 
-  // NS_DECL_IDOMCSSSTYLEDECLARATION
-  NS_IMETHOD    GetCssText(nsAString& aCssText);
-  NS_IMETHOD    SetCssText(const nsAString& aCssText);
-  NS_IMETHOD    GetLength(PRUint32* aLength);
-  NS_IMETHOD    GetParentRule(nsIDOMCSSRule** aParentRule);
-  NS_IMETHOD    GetPropertyValue(const nsAString& aPropertyName,
-                                 nsAString& aReturn);
-  NS_IMETHOD    GetPropertyCSSValue(const nsAString& aPropertyName,
-                                    nsIDOMCSSValue** aReturn);
-  NS_IMETHOD    RemoveProperty(const nsAString& aPropertyName,
-                               nsAString& aReturn) = 0;
-  NS_IMETHOD    GetPropertyPriority(const nsAString& aPropertyName,
-                                    nsAString& aReturn);
-  NS_IMETHOD    SetProperty(const nsAString& aPropertyName,
-                            const nsAString& aValue,
-                            const nsAString& aPriority);
-  NS_IMETHOD    Item(PRUint32 aIndex, nsAString& aReturn);
-
+  NS_DECL_NSIDOMCSSSTYLEDECLARATION
 
   virtual void DropReference() = 0;
-  // XXX DeCOMify this, so that |nsCSSDeclaration*| is the return type.
+protected:
+  // Always fills in the out parameter, even on failure, and if the out
+  // parameter is null the nsresult will be the correct thing to
+  // propagate.
   virtual nsresult GetCSSDeclaration(nsCSSDeclaration **aDecl,
                                      PRBool aAllocate) = 0;
-  virtual nsresult ParsePropertyValue(const nsAString& aPropName,
-                                      const nsAString& aPropValue) = 0;
-  virtual nsresult ParseDeclaration(const nsAString& aDecl,
-                                    PRBool aParseOnlyOneDecl,
-                                    PRBool aClearOldDecl) = 0;
   virtual nsresult GetParent(nsISupports **aParent) = 0;
+  virtual nsresult DeclarationChanged() = 0;
+  
+  // This will only fail if it can't get a parser.  This means it can
+  // return NS_OK without aURI or aCSSLoader being initialized.
+  virtual nsresult GetCSSParsingEnvironment(nsIURI** aBaseURI,
+                                            nsICSSLoader** aCSSLoader,
+                                            nsICSSParser** aCSSParser) = 0;
+
+  nsresult ParsePropertyValue(const nsAString& aPropName,
+                              const nsAString& aPropValue);
+  nsresult ParseDeclaration(const nsAString& aDecl,
+                            PRBool aParseOnlyOneDecl, PRBool aClearOldDecl);
   
 protected:
   virtual ~nsDOMCSSDeclaration();
diff --git a/mozilla/layout/style/nsICSSGroupRule.h b/mozilla/layout/style/nsICSSGroupRule.h
index f76a34bb920..210f8287fdc 100644
--- a/mozilla/layout/style/nsICSSGroupRule.h
+++ b/mozilla/layout/style/nsICSSGroupRule.h
@@ -59,14 +59,13 @@ public:
   NS_IMETHOD  EnumerateRulesForwards(nsISupportsArrayEnumFunc aFunc, void * aData) const = 0;
 
   /*
-   * The next two methods (DeleteStyleRuleAt and InsertStyleRulesAt)
-   * should never be called unless you have first called WillDirty()
-   * on the parent stylesheet.  After they are called, DidDirty()
-   * needs to be called on the sheet
+   * The next three methods should never be called unless you have first
+   * called WillDirty() on the parent stylesheet.  After they are
+   * called, DidDirty() needs to be called on the sheet.
    */
   NS_IMETHOD  DeleteStyleRuleAt(PRUint32 aIndex) = 0;
   NS_IMETHOD  InsertStyleRulesAt(PRUint32 aIndex, nsISupportsArray* aRules) = 0;
-
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew) = 0;
    
 };
 
diff --git a/mozilla/layout/style/nsICSSStyleRule.h b/mozilla/layout/style/nsICSSStyleRule.h
index c19044afac5..94afae748e4 100644
--- a/mozilla/layout/style/nsICSSStyleRule.h
+++ b/mozilla/layout/style/nsICSSStyleRule.h
@@ -201,7 +201,18 @@ public:
   virtual void SetLineNumber(PRUint32 aLineNumber) = 0;
 
   virtual nsCSSDeclaration* GetDeclaration(void) const = 0;
-  virtual void SetDeclaration(nsCSSDeclaration* aDeclaration) = 0;
+
+  /**
+   * Return a new |nsIStyleRule| instance that replaces the current one,
+   * due to a change in the |nsCSSDeclaration|.  Due to the
+   * |nsIStyleRule| contract of immutability, this must be called if the
+   * declaration is modified.
+   *
+   * |DeclarationChanged| handles replacing the object in the container
+   * sheet or group rule if |aHandleContainer| is true.
+   */
+  virtual already_AddRefed<nsICSSStyleRule>
+    DeclarationChanged(PRBool aHandleContainer) = 0;
 
   virtual already_AddRefed<nsIStyleRule> GetImportantRule(void) = 0;
 
@@ -211,6 +222,7 @@ public:
 
 nsresult
 NS_NewCSSStyleRule(nsICSSStyleRule** aInstancePtrResult,
-                   nsCSSSelectorList* aSelector);
+                   nsCSSSelectorList* aSelector,
+                   nsCSSDeclaration* aDeclaration);
 
 #endif /* nsICSSStyleRule_h___ */
diff --git a/mozilla/layout/style/nsICSSStyleSheet.h b/mozilla/layout/style/nsICSSStyleSheet.h
index 6ccaa54f77d..7c863be0dba 100644
--- a/mozilla/layout/style/nsICSSStyleSheet.h
+++ b/mozilla/layout/style/nsICSSStyleSheet.h
@@ -64,12 +64,14 @@ public:
 
   NS_IMETHOD  PrependStyleRule(nsICSSRule* aRule) = 0;
   NS_IMETHOD  AppendStyleRule(nsICSSRule* aRule) = 0;
+  NS_IMETHOD  ReplaceStyleRule(nsICSSRule* aOld, nsICSSRule* aNew) = 0;
 
   NS_IMETHOD  StyleRuleCount(PRInt32& aCount) const = 0;
   NS_IMETHOD  GetStyleRuleAt(PRInt32 aIndex, nsICSSRule*& aRule) const = 0;
 
   NS_IMETHOD  DeleteRuleFromGroup(nsICSSGroupRule* aGroup, PRUint32 aIndex) = 0;
   NS_IMETHOD  InsertRuleIntoGroup(const nsAString & aRule, nsICSSGroupRule* aGroup, PRUint32 aIndex, PRUint32* _retval) = 0;
+  NS_IMETHOD  ReplaceRuleInGroup(nsICSSGroupRule* aGroup, nsICSSRule* aOld, nsICSSRule* aNew) = 0;
 
   NS_IMETHOD  StyleSheetCount(PRInt32& aCount) const = 0;
   NS_IMETHOD  GetStyleSheetAt(PRInt32 aIndex, nsICSSStyleSheet*& aSheet) const = 0;
diff --git a/mozilla/layout/style/nsIStyleRule.h b/mozilla/layout/style/nsIStyleRule.h
index d10791c3e38..d67723f1241 100644
--- a/mozilla/layout/style/nsIStyleRule.h
+++ b/mozilla/layout/style/nsIStyleRule.h
@@ -51,13 +51,54 @@ struct nsRuleData;
 #define NS_ISTYLE_RULE_IID     \
 {0x40ae5c90, 0xad6a, 0x11d1, {0x80, 0x31, 0x00, 0x60, 0x08, 0x15, 0x9b, 0x5a}}
 
+/**
+ * An object implementing |nsIStyleRule| (henceforth, a rule) represents
+ * immutable stylistic information that either applies or does not apply
+ * to a given element.  It belongs to an object or group of objects that
+ * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
+ * sheet).
+ *
+ * A rule becomes relevant to the computation of style data when
+ * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
+ * points to the rule.  (A rule node, |nsRuleNode|, is a node in the
+ * rule tree, which is a lexicographic tree indexed by rules.  The path
+ * from the root of the rule tree to the |nsRuleNode| for a given
+ * |nsStyleContext| contains exactly the rules that match the element
+ * that the style context is for, in priority (weight, origin,
+ * specificity) order.)
+ *
+ * The computation of style data uses the rule tree, which calls
+ * |nsIStyleRule::MapRuleInfoInto| below.
+ *
+ * It is worth emphasizing that the data represented by a rule
+ * implementation are immutable.  When the data need to be changed, a
+ * new rule object must be created.  Failing to do this will lead to
+ * bugs in the handling of dynamic style changes, since the rule tree
+ * caches the results of |MapRuleInfoInto|.
+ *
+ * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
+ * to typically being owned by their sheet), which are in turn garbage
+ * collected (with the garbage collection roots being style contexts).
+ */
+
+
 class nsIStyleRule : public nsISupports {
 public:
   NS_DEFINE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
 
   NS_IMETHOD GetStyleSheet(nsIStyleSheet*& aSheet) const = 0;
 
-  // The new mapping function.
+  /**
+   * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
+   * data represented by the rule that:
+   *   + are relevant for |aRuleData->mSID| (the style struct ID)
+   *   + are not already filled into the data struct
+   * into the appropriate data struct in |aRuleData|.  It is important
+   * that only empty data are filled in, since the rule tree is walked
+   * from highest priority rule to least, so that the walk can stop if
+   * all needed data are found.  Thus overwriting non-empty data will
+   * break CSS cascading rules.
+   */
   NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData)=0;
 
 #ifdef DEBUG
diff --git a/mozilla/layout/style/nsRuleNode.cpp b/mozilla/layout/style/nsRuleNode.cpp
index 1bb258619e1..f26df07f013 100644
--- a/mozilla/layout/style/nsRuleNode.cpp
+++ b/mozilla/layout/style/nsRuleNode.cpp
@@ -553,74 +553,31 @@ nsRuleNode::PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched)
   return NS_OK;
 }
 
-nsresult
-nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
-{
-  NS_ASSERTION(aRule, "you should be using ClearCachedDataInSubtree");
-
-  nsRuleNode* ruleDest = this;
-  while (ruleDest) {
-    if (ruleDest->mRule == aRule)
-      break;
-    ruleDest = ruleDest->mParent;
-  }
-
-  if (ruleDest) {
-    NS_ASSERTION(ruleDest->mParent, "node must not be root");
-
-    // The rule was contained along our branch.  We need to blow away
-    // all cached data along this path.  Note that, because of the definition
-    // of inline style, all nodes along this path must have exactly one child.  This
-    // is not a bushy subtree, and so we know that by clearing this path, we've
-    // invalidated everything that we need to.
-    // XXXldb What about !important :hover rules, and such?
-    nsRuleNode* curr = this;
-    while (curr) {
-      curr->mNoneBits &= ~NS_STYLE_INHERIT_MASK;
-      curr->mDependentBits &= ~NS_STYLE_INHERIT_MASK;
-      if (curr->mStyleData.mResetData || curr->mStyleData.mInheritedData)
-        curr->mStyleData.Destroy(0, mPresContext);
-
-      if (curr == ruleDest)
-        break;
-
-      curr = curr->mParent;
-    }
-  }
-
-  return NS_OK;
-}
-
 PR_STATIC_CALLBACK(PLDHashOperator)
-ClearCachedDataInSubtreeHelper(PLDHashTable *table, PLDHashEntryHdr *hdr,
+ClearStyleDataHelper(PLDHashTable *table, PLDHashEntryHdr *hdr,
                                PRUint32 number, void *arg)
 {
   ChildrenHashEntry *entry = NS_STATIC_CAST(ChildrenHashEntry*, hdr);
-  nsIStyleRule* rule = NS_STATIC_CAST(nsIStyleRule*, arg);
-  entry->mRuleNode->ClearCachedDataInSubtree(rule);
+  entry->mRuleNode->ClearStyleData();
   return PL_DHASH_NEXT;
 }
 
 nsresult
-nsRuleNode::ClearCachedDataInSubtree(nsIStyleRule* aRule)
+nsRuleNode::ClearStyleData()
 {
-  if (aRule == nsnull || mRule == aRule) {
-    // We have a match.  Blow away all data stored at this node.
-    if (mStyleData.mResetData || mStyleData.mInheritedData)
-      mStyleData.Destroy(0, mPresContext);
+  // Blow away all data stored at this node.
+  if (mStyleData.mResetData || mStyleData.mInheritedData)
+    mStyleData.Destroy(0, mPresContext);
 
-    mNoneBits &= ~NS_STYLE_INHERIT_MASK;
-    mDependentBits &= ~NS_STYLE_INHERIT_MASK;
-
-    aRule = nsnull;  // Cause everything to be blown away in the descendants.
-  }
+  mNoneBits &= ~NS_STYLE_INHERIT_MASK;
+  mDependentBits &= ~NS_STYLE_INHERIT_MASK;
 
   if (ChildrenAreHashed())
     PL_DHashTableEnumerate(ChildrenHash(),
-                           ClearCachedDataInSubtreeHelper, aRule);
+                           ClearStyleDataHelper, nsnull);
   else
     for (nsRuleList* curr = ChildrenList(); curr; curr = curr->mNext)
-      curr->mRuleNode->ClearCachedDataInSubtree(aRule);
+      curr->mRuleNode->ClearStyleData();
 
   return NS_OK;
 }
@@ -649,11 +606,7 @@ nsRuleNode::PropagateNoneBit(PRUint32 aBit, nsRuleNode* aHighestNode)
 inline void
 nsRuleNode::PropagateDependentBit(PRUint32 aBit, nsRuleNode* aHighestNode)
 {
-  if (mDependentBits & aBit)
-    return; // Already set.
-
-  nsRuleNode* curr = this;
-  while (curr != aHighestNode) {
+  for (nsRuleNode* curr = this; curr != aHighestNode; curr = curr->mParent) {
     if (curr->mDependentBits & aBit) {
 #ifdef DEBUG
       while (curr != aHighestNode) {
@@ -665,7 +618,6 @@ nsRuleNode::PropagateDependentBit(PRUint32 aBit, nsRuleNode* aHighestNode)
     }
 
     curr->mDependentBits |= aBit;
-    curr = curr->mParent;
   }
 }
 
@@ -1148,223 +1100,223 @@ nsRuleNode::CheckSpecifiedProperties(const nsStyleStructID aSID,
 }
 
 const nsStyleStruct*
-nsRuleNode::GetDisplayData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetDisplayData(nsStyleContext* aContext)
 {
   nsRuleDataDisplay displayData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Display, mPresContext, aContext);
   ruleData.mDisplayData = &displayData;
 
-  return WalkRuleTree(eStyleStruct_Display, aContext, &ruleData, &displayData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Display, aContext, &ruleData, &displayData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetVisibilityData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetVisibilityData(nsStyleContext* aContext)
 {
   nsRuleDataDisplay displayData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Visibility, mPresContext, aContext);
   ruleData.mDisplayData = &displayData;
 
-  return WalkRuleTree(eStyleStruct_Visibility, aContext, &ruleData, &displayData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Visibility, aContext, &ruleData, &displayData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTextData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTextData(nsStyleContext* aContext)
 {
   nsRuleDataText textData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Text, mPresContext, aContext);
   ruleData.mTextData = &textData;
 
-  return WalkRuleTree(eStyleStruct_Text, aContext, &ruleData, &textData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Text, aContext, &ruleData, &textData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTextResetData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTextResetData(nsStyleContext* aContext)
 {
   nsRuleDataText textData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_TextReset, mPresContext, aContext);
   ruleData.mTextData = &textData;
 
-  return WalkRuleTree(eStyleStruct_TextReset, aContext, &ruleData, &textData, aComputeData);
+  return WalkRuleTree(eStyleStruct_TextReset, aContext, &ruleData, &textData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetUserInterfaceData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetUserInterfaceData(nsStyleContext* aContext)
 {
   nsRuleDataUserInterface uiData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_UserInterface, mPresContext, aContext);
   ruleData.mUserInterfaceData = &uiData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UserInterface, aContext, &ruleData, &uiData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UserInterface, aContext, &ruleData, &uiData);
   uiData.mCursor = nsnull;
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetUIResetData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetUIResetData(nsStyleContext* aContext)
 {
   nsRuleDataUserInterface uiData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_UIReset, mPresContext, aContext);
   ruleData.mUserInterfaceData = &uiData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UIReset, aContext, &ruleData, &uiData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_UIReset, aContext, &ruleData, &uiData);
   uiData.mKeyEquivalent = nsnull;
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetFontData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetFontData(nsStyleContext* aContext)
 {
   nsRuleDataFont fontData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Font, mPresContext, aContext);
   ruleData.mFontData = &fontData;
 
-  return WalkRuleTree(eStyleStruct_Font, aContext, &ruleData, &fontData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Font, aContext, &ruleData, &fontData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetColorData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetColorData(nsStyleContext* aContext)
 {
   nsRuleDataColor colorData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Color, mPresContext, aContext);
   ruleData.mColorData = &colorData;
 
-  return WalkRuleTree(eStyleStruct_Color, aContext, &ruleData, &colorData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Color, aContext, &ruleData, &colorData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetBackgroundData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetBackgroundData(nsStyleContext* aContext)
 {
   nsRuleDataColor colorData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Background, mPresContext, aContext);
   ruleData.mColorData = &colorData;
 
-  return WalkRuleTree(eStyleStruct_Background, aContext, &ruleData, &colorData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Background, aContext, &ruleData, &colorData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetMarginData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetMarginData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Margin, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Margin, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Margin, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetBorderData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetBorderData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Border, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Border, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Border, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetPaddingData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetPaddingData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Padding, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Padding, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Padding, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetOutlineData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetOutlineData(nsStyleContext* aContext)
 {
   nsRuleDataMargin marginData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Outline, mPresContext, aContext);
   ruleData.mMarginData = &marginData;
 
-  return WalkRuleTree(eStyleStruct_Outline, aContext, &ruleData, &marginData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Outline, aContext, &ruleData, &marginData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetListData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetListData(nsStyleContext* aContext)
 {
   nsRuleDataList listData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_List, mPresContext, aContext);
   ruleData.mListData = &listData;
 
-  return WalkRuleTree(eStyleStruct_List, aContext, &ruleData, &listData, aComputeData);
+  return WalkRuleTree(eStyleStruct_List, aContext, &ruleData, &listData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetPositionData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetPositionData(nsStyleContext* aContext)
 {
   nsRuleDataPosition posData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Position, mPresContext, aContext);
   ruleData.mPositionData = &posData;
 
-  return WalkRuleTree(eStyleStruct_Position, aContext, &ruleData, &posData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Position, aContext, &ruleData, &posData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTableData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTableData(nsStyleContext* aContext)
 {
   nsRuleDataTable tableData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Table, mPresContext, aContext);
   ruleData.mTableData = &tableData;
 
-  return WalkRuleTree(eStyleStruct_Table, aContext, &ruleData, &tableData, aComputeData);
+  return WalkRuleTree(eStyleStruct_Table, aContext, &ruleData, &tableData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetTableBorderData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetTableBorderData(nsStyleContext* aContext)
 {
   nsRuleDataTable tableData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_TableBorder, mPresContext, aContext);
   ruleData.mTableData = &tableData;
 
-  return WalkRuleTree(eStyleStruct_TableBorder, aContext, &ruleData, &tableData, aComputeData);
+  return WalkRuleTree(eStyleStruct_TableBorder, aContext, &ruleData, &tableData);
 }
 
 const nsStyleStruct*
-nsRuleNode::GetContentData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetContentData(nsStyleContext* aContext)
 {
   nsRuleDataContent contentData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Content, mPresContext, aContext);
   ruleData.mContentData = &contentData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Content, aContext, &ruleData, &contentData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Content, aContext, &ruleData, &contentData);
   contentData.mCounterIncrement = contentData.mCounterReset = nsnull;
   contentData.mContent = nsnull; // We are sharing with some style rule.  It really owns the data.
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetQuotesData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetQuotesData(nsStyleContext* aContext)
 {
   nsRuleDataContent contentData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_Quotes, mPresContext, aContext);
   ruleData.mContentData = &contentData;
 
-  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Quotes, aContext, &ruleData, &contentData, aComputeData);
+  const nsStyleStruct* res = WalkRuleTree(eStyleStruct_Quotes, aContext, &ruleData, &contentData);
   contentData.mQuotes = nsnull; // We are sharing with some style rule.  It really owns the data.
   return res;
 }
 
 const nsStyleStruct*
-nsRuleNode::GetXULData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetXULData(nsStyleContext* aContext)
 {
   nsRuleDataXUL xulData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_XUL, mPresContext, aContext);
   ruleData.mXULData = &xulData;
 
-  return WalkRuleTree(eStyleStruct_XUL, aContext, &ruleData, &xulData, aComputeData);
+  return WalkRuleTree(eStyleStruct_XUL, aContext, &ruleData, &xulData);
 }
 
 #ifdef MOZ_SVG
 const nsStyleStruct*
-nsRuleNode::GetSVGData(nsStyleContext* aContext, PRBool aComputeData)
+nsRuleNode::GetSVGData(nsStyleContext* aContext)
 {
   nsRuleDataSVG svgData; // Declare a struct with null CSS values.
   nsRuleData ruleData(eStyleStruct_SVG, mPresContext, aContext);
   ruleData.mSVGData = &svgData;
 
-  return WalkRuleTree(eStyleStruct_SVG, aContext, &ruleData, &svgData, aComputeData);
+  return WalkRuleTree(eStyleStruct_SVG, aContext, &ruleData, &svgData);
 }
 #endif
 
@@ -1372,8 +1324,7 @@ const nsStyleStruct*
 nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
                          nsStyleContext* aContext, 
                          nsRuleData* aRuleData,
-                         nsRuleDataStruct* aSpecificData,
-                         PRBool aComputeData)
+                         nsRuleDataStruct* aSpecificData)
 {
   // We start at the most specific rule in the tree.  
   nsStyleStruct* startStruct = nsnull;
@@ -1496,9 +1447,6 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
   }
 
   // We need to compute the data from the information that the rules specified.
-  if (!aComputeData)
-    return nsnull;
-  
   ComputeStyleDataFn fn = gComputeStyleDataFn[aSID];
   const nsStyleStruct* res = (this->*fn)(startStruct, *aSpecificData, aContext, highestNode, detail,
                                          !aRuleData->mCanStoreInRuleTree);
@@ -4491,14 +4439,17 @@ nsRuleNode::GetStyleData(nsStyleStructID aSID,
     NS_NOTREACHED("dependent bits set but no cached struct present");
   }
 
+  if (!aComputeData)
+    return nsnull;
+
   // Nothing is cached.  We'll have to delve further and examine our rules.
   GetStyleDataFn fn = gGetStyleDataFn[aSID];
   if (!fn) {
     NS_NOTREACHED("unknown style struct requested");
     return nsnull;
   }
-  data = (this->*fn)(aContext, aComputeData);
-  if (data || !aComputeData)
+  data = (this->*fn)(aContext);
+  if (data)
     return data;
 
   NS_NOTREACHED("could not create style struct");
diff --git a/mozilla/layout/style/nsRuleNode.h b/mozilla/layout/style/nsRuleNode.h
index b5df7848fdd..c2532afc8cb 100644
--- a/mozilla/layout/style/nsRuleNode.h
+++ b/mozilla/layout/style/nsRuleNode.h
@@ -410,8 +410,7 @@ protected:
 
   const nsStyleStruct* WalkRuleTree(const nsStyleStructID aSID, nsStyleContext* aContext, 
                                     nsRuleData* aRuleData,
-                                    nsRuleDataStruct* aSpecificData,
-                                    PRBool aComputeData);
+                                    nsRuleDataStruct* aSpecificData);
 
   const nsStyleStruct* ComputeDisplayData(nsStyleStruct* aStartDisplay, const nsRuleDataStruct& aDisplayData, 
                                           nsStyleContext* aContext, nsRuleNode* aHighestNode,
@@ -504,31 +503,31 @@ protected:
   inline RuleDetail CheckSpecifiedProperties(const nsStyleStructID aSID, const nsRuleDataStruct& aRuleDataStruct);
 
   const nsStyleStruct* GetParentData(const nsStyleStructID aSID);
-  const nsStyleStruct* GetDisplayData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetVisibilityData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetFontData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetColorData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetBackgroundData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetMarginData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetBorderData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetPaddingData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetOutlineData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetListData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetPositionData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTableData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTableBorderData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetContentData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetQuotesData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTextData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetTextResetData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetUserInterfaceData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetUIResetData(nsStyleContext* aContext, PRBool aComputeData);
-  const nsStyleStruct* GetXULData(nsStyleContext* aContext, PRBool aComputeData);
+  const nsStyleStruct* GetDisplayData(nsStyleContext* aContext);
+  const nsStyleStruct* GetVisibilityData(nsStyleContext* aContext);
+  const nsStyleStruct* GetFontData(nsStyleContext* aContext);
+  const nsStyleStruct* GetColorData(nsStyleContext* aContext);
+  const nsStyleStruct* GetBackgroundData(nsStyleContext* aContext);
+  const nsStyleStruct* GetMarginData(nsStyleContext* aContext);
+  const nsStyleStruct* GetBorderData(nsStyleContext* aContext);
+  const nsStyleStruct* GetPaddingData(nsStyleContext* aContext);
+  const nsStyleStruct* GetOutlineData(nsStyleContext* aContext);
+  const nsStyleStruct* GetListData(nsStyleContext* aContext);
+  const nsStyleStruct* GetPositionData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTableData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTableBorderData(nsStyleContext* aContext);
+  const nsStyleStruct* GetContentData(nsStyleContext* aContext);
+  const nsStyleStruct* GetQuotesData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTextData(nsStyleContext* aContext);
+  const nsStyleStruct* GetTextResetData(nsStyleContext* aContext);
+  const nsStyleStruct* GetUserInterfaceData(nsStyleContext* aContext);
+  const nsStyleStruct* GetUIResetData(nsStyleContext* aContext);
+  const nsStyleStruct* GetXULData(nsStyleContext* aContext);
 #ifdef MOZ_SVG
-  const nsStyleStruct* GetSVGData(nsStyleContext* aContext, PRBool aComputeData);
+  const nsStyleStruct* GetSVGData(nsStyleContext* aContext);
 #endif
 
-  typedef const nsStyleStruct* (nsRuleNode::*GetStyleDataFn)(nsStyleContext*, PRBool);
+  typedef const nsStyleStruct* (nsRuleNode::*GetStyleDataFn)(nsStyleContext*);
   static GetStyleDataFn gGetStyleDataFn[];
 
 public:
@@ -557,8 +556,7 @@ public:
     return mPresContext;
   }
 
-  nsresult ClearCachedData(nsIStyleRule* aRule);
-  nsresult ClearCachedDataInSubtree(nsIStyleRule* aRule);
+  nsresult ClearStyleData();
   nsresult GetPresContext(nsIPresContext** aResult);
   nsresult PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched);
   const nsStyleStruct* GetStyleData(nsStyleStructID aSID, 
diff --git a/mozilla/layout/style/nsStyleContext.cpp b/mozilla/layout/style/nsStyleContext.cpp
index 810984b4290..f6daeb03e54 100644
--- a/mozilla/layout/style/nsStyleContext.cpp
+++ b/mozilla/layout/style/nsStyleContext.cpp
@@ -396,27 +396,20 @@ nsStyleContext::ApplyStyleFixups(nsIPresContext* aPresContext)
 }
 
 void
-nsStyleContext::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule)
+nsStyleContext::ClearStyleData(nsIPresContext* aPresContext)
 {
-  PRBool matched = PR_TRUE;
-  if (aRule)
-    mRuleNode->PathContainsRule(aRule, &matched);
-  
-  if (matched) {
-    // First we need to clear out all of our style data.
-    if (mCachedStyleData.mResetData || mCachedStyleData.mInheritedData)
-      mCachedStyleData.Destroy(mBits, aPresContext);
+  // First we need to clear out all of our style data.
+  if (mCachedStyleData.mResetData || mCachedStyleData.mInheritedData)
+    mCachedStyleData.Destroy(mBits, aPresContext);
 
-    mBits = 0; // Clear all bits.
-    aRule = nsnull; // Force all structs to be blown away in the children.
-  }
+  mBits = 0; // Clear all bits.
 
   ApplyStyleFixups(aPresContext);
 
   if (mChild) {
     nsStyleContext* child = mChild;
     do {
-      child->ClearStyleData(aPresContext, aRule);
+      child->ClearStyleData(aPresContext);
       child = child->mNextSibling;
     } while (mChild != child);
   }
@@ -424,7 +417,7 @@ nsStyleContext::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule
   if (mEmptyChild) {
     nsStyleContext* child = mEmptyChild;
     do {
-      child->ClearStyleData(aPresContext, aRule);
+      child->ClearStyleData(aPresContext);
       child = child->mNextSibling;
     } while (mEmptyChild != child);
   }
diff --git a/mozilla/layout/style/nsStyleContext.h b/mozilla/layout/style/nsStyleContext.h
index 1f480293632..be3629234e8 100644
--- a/mozilla/layout/style/nsStyleContext.h
+++ b/mozilla/layout/style/nsStyleContext.h
@@ -139,7 +139,7 @@ public:
 
   nsStyleStruct* GetUniqueStyleData(nsIPresContext* aPresContext, const nsStyleStructID& aSID);
 
-  void ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule);
+  void ClearStyleData(nsIPresContext* aPresContext);
 
   nsChangeHint CalcStyleDifference(nsStyleContext* aOther);
 
diff --git a/mozilla/layout/style/nsStyleSet.cpp b/mozilla/layout/style/nsStyleSet.cpp
index be03afc5468..9baf2b190e9 100644
--- a/mozilla/layout/style/nsStyleSet.cpp
+++ b/mozilla/layout/style/nsStyleSet.cpp
@@ -195,7 +195,7 @@ public:
 
   virtual nsresult GetRuleTree(nsRuleNode** aResult);
   
-  virtual nsresult ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule);
+  virtual nsresult ClearStyleData(nsIPresContext* aPresContext);
 
   virtual nsresult GetStyleFrameConstruction(nsIStyleFrameConstruction** aResult) {
     *aResult = mFrameConstructor;
@@ -254,20 +254,6 @@ public:
                               PRInt32 aModType, 
                               nsChangeHint aHint); // See nsStyleConsts fot hint values
 
-  // xxx style rules enumeration
-
-  // Style change notifications
-  NS_IMETHOD StyleRuleChanged(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule,
-                              nsChangeHint aHint); // See nsStyleConsts fot hint values
-  NS_IMETHOD StyleRuleAdded(nsIPresContext* aPresContext,
-                            nsIStyleSheet* aStyleSheet,
-                            nsIStyleRule* aStyleRule);
-  NS_IMETHOD StyleRuleRemoved(nsIPresContext* aPresContext,
-                              nsIStyleSheet* aStyleSheet,
-                              nsIStyleRule* aStyleRule);
-
   // Notification that we were unable to render a replaced element.
   NS_IMETHOD CantRenderReplacedElement(nsIPresContext* aPresContext,
                                        nsIFrame*       aFrame);
@@ -1504,30 +1490,13 @@ StyleSetImpl::GetDefaultStyleData()
 }
 
 nsresult
-StyleSetImpl::ClearStyleData(nsIPresContext* aPresContext, nsIStyleRule* aRule)
+StyleSetImpl::ClearStyleData(nsIPresContext* aPresContext)
 {
-  // XXXdwh This is not terribly fast, but fortunately this case is rare (and often a full tree
-  // invalidation anyway).  Improving performance here would involve a footprint
-  // increase.  Mappings from rule nodes to their associated style contexts as well as
-  // mappings from rules to their associated rule nodes would enable us to avoid the two
-  // tree walks that occur here.
-  
-  // Crawl the entire rule tree and blow away all data for rule nodes (and their descendants)
-  // that have the given rule.
   if (mRuleTree)
-    mRuleTree->ClearCachedDataInSubtree(aRule);
-  
-  // We need to crawl the entire style context tree, and for each style context we need 
-  // to see if the specified rule is matched.  If so, that context and all its descendant
-  // contexts must have their data wiped.
-  nsCOMPtr<nsIPresShell> shell;
-  aPresContext->GetShell(getter_AddRefs(shell));
-  nsIFrame* rootFrame;
-  shell->GetRootFrame(&rootFrame);
-  if (rootFrame) {
-    nsStyleContext* rootContext = rootFrame->GetStyleContext();
-    if (rootContext)
-      rootContext->ClearStyleData(aPresContext, aRule);
+    mRuleTree->ClearStyleData();
+
+  for (PRInt32 i = mRoots.Count() - 1; i >= 0; --i) {
+    NS_STATIC_CAST(nsStyleContext*,mRoots[i])->ClearStyleData(aPresContext);
   }
 
   return NS_OK;
@@ -1761,33 +1730,6 @@ StyleSetImpl::AttributeChanged(nsIPresContext* aPresContext,
                                              aNameSpaceID, aAttribute, aModType, aHint);
 }
 
-
-// Style change notifications
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleChanged(nsIPresContext* aPresContext,
-                               nsIStyleSheet* aStyleSheet,
-                               nsIStyleRule* aStyleRule,
-                               nsChangeHint aHint)
-{
-  return mFrameConstructor->StyleRuleChanged(aPresContext, aStyleSheet, aStyleRule, aHint);
-}
-
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleAdded(nsIPresContext* aPresContext,
-                             nsIStyleSheet* aStyleSheet,
-                             nsIStyleRule* aStyleRule)
-{
-  return mFrameConstructor->StyleRuleAdded(aPresContext, aStyleSheet, aStyleRule);
-}
-
-NS_IMETHODIMP
-StyleSetImpl::StyleRuleRemoved(nsIPresContext* aPresContext,
-                               nsIStyleSheet* aStyleSheet,
-                               nsIStyleRule* aStyleRule)
-{
-  return mFrameConstructor->StyleRuleRemoved(aPresContext, aStyleSheet, aStyleRule);
-}
-
 NS_IMETHODIMP
 StyleSetImpl::CantRenderReplacedElement(nsIPresContext* aPresContext,
                                         nsIFrame*       aFrame)