diff --git a/mozilla/content/base/public/nsIDocument.h b/mozilla/content/base/public/nsIDocument.h
index a671217a583..74ac4b104b6 100644
--- a/mozilla/content/base/public/nsIDocument.h
+++ b/mozilla/content/base/public/nsIDocument.h
@@ -53,7 +53,6 @@
 #include "nsILoadGroup.h"
 #include "nsReadableUtils.h"
 #include "nsCRT.h"
-#include <stdio.h>   // for FILE definition
 
 class nsIAtom;
 class nsIContent;
diff --git a/mozilla/content/base/src/nsDocument.cpp b/mozilla/content/base/src/nsDocument.cpp
index d783714c8a9..4957c8352ed 100644
--- a/mozilla/content/base/src/nsDocument.cpp
+++ b/mozilla/content/base/src/nsDocument.cpp
@@ -1519,7 +1519,9 @@ nsDocument::SetStyleSheetApplicableState(nsIStyleSheet* aSheet,
     }
   } else {
     // We still need to notify the style set of the state change, because
-    // this will invalidate some of the rule processor data.
+    // this will invalidate some of the rule processor data.  We do this
+    // here instead of in the pres shell because we _don't_ want to do this
+    // for document style sheets.
 
     PRInt32 count = mPresShells.Count();
     PRInt32 indx;
@@ -1647,14 +1649,6 @@ nsDocument::RemoveObserver(nsIDocumentObserver* aObserver)
 void
 nsDocument::BeginUpdate(nsUpdateType aUpdateType)
 {
-  if (aUpdateType & UPDATE_STYLE) {
-    PRInt32 shellCount = mPresShells.Count();
-    for (PRInt32 j = 0; j < shellCount; ++j) {
-      NS_STATIC_CAST(nsIPresShell*, mPresShells.ElementAt(j))->StyleSet()->
-        BeginUpdate();
-    }
-  }
-
   PRInt32 i;
   for (i = mObservers.Count() - 1; i >= 0; --i) {
     nsIDocumentObserver* observer = (nsIDocumentObserver*) mObservers[i];
@@ -1665,14 +1659,6 @@ nsDocument::BeginUpdate(nsUpdateType aUpdateType)
 void
 nsDocument::EndUpdate(nsUpdateType aUpdateType)
 {
-  if (aUpdateType & UPDATE_STYLE) {
-    PRInt32 shellCount = mPresShells.Count();
-    for (PRInt32 j = 0; j < shellCount; ++j) {
-      NS_STATIC_CAST(nsIPresShell*, mPresShells.ElementAt(j))->StyleSet()->
-        EndUpdate();
-    }
-  }
-
   PRInt32 i;
   for (i = mObservers.Count() - 1; i >= 0; --i) {
     nsIDocumentObserver* observer = (nsIDocumentObserver*) mObservers[i];
diff --git a/mozilla/content/base/src/nsDocumentViewer.cpp b/mozilla/content/base/src/nsDocumentViewer.cpp
index 3e01343df94..ec28baeaf64 100644
--- a/mozilla/content/base/src/nsDocumentViewer.cpp
+++ b/mozilla/content/base/src/nsDocumentViewer.cpp
@@ -639,8 +639,8 @@ nsresult
 DocumentViewerImpl::InitPresentationStuff(PRBool aDoInitialReflow)
 {
   // Create the style set...
-  nsStyleSet *styleSet;
-  nsresult rv = CreateStyleSet(mDocument, &styleSet);
+  nsAutoPtr<nsStyleSet> styleSet;
+  nsresult rv = CreateStyleSet(mDocument, getter_Transfers(styleSet));
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Now make the shell for the document
@@ -649,6 +649,9 @@ DocumentViewerImpl::InitPresentationStuff(PRBool aDoInitialReflow)
 
   NS_ENSURE_SUCCESS(rv, rv);
 
+  // The pres shell owns the style set now.
+  styleSet.forget();
+
   if (aDoInitialReflow) {
     // Since InitialReflow() will create frames for *all* items
     // that are currently in the document tree, we need to flush
@@ -1191,8 +1194,8 @@ DocumentViewerImpl::SetDOMDocument(nsIDOMDocument *aDocument)
   if (mPresContext) {
     // 3) Create a new style set for the document
 
-    nsStyleSet *styleSet;
-    rv = CreateStyleSet(mDocument, &styleSet);
+    nsAutoPtr<nsStyleSet> styleSet;
+    rv = CreateStyleSet(mDocument, getter_Transfers(styleSet));
     if (NS_FAILED(rv))
       return rv;
 
@@ -1200,6 +1203,9 @@ DocumentViewerImpl::SetDOMDocument(nsIDOMDocument *aDocument)
                              getter_AddRefs(mPresShell));
     NS_ENSURE_SUCCESS(rv, rv);
 
+    // The pres shell owns the style set now.
+    styleSet.forget();
+
     mPresShell->BeginObservingDocument();
 
     // 4) Register the focus listener on the new document
@@ -1594,7 +1600,7 @@ DocumentViewerImpl::CreateStyleSet(nsIDocument* aDocument,
     NS_WARNING("unable to load UA style sheet");
   }
 
-  nsStyleSet *styleSet = new nsStyleSet();
+  nsAutoPtr<nsStyleSet> styleSet(new nsStyleSet());
   if (!styleSet) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -1663,6 +1669,7 @@ DocumentViewerImpl::CreateStyleSet(nsIDocument* aDocument,
 
   styleSet->EndUpdate();
   *aStyleSet = styleSet;
+  styleSet.forget();
   return NS_OK;
 }
 
diff --git a/mozilla/content/base/src/nsPrintEngine.cpp b/mozilla/content/base/src/nsPrintEngine.cpp
index 151e4cc9e08..a4c8dc21387 100644
--- a/mozilla/content/base/src/nsPrintEngine.cpp
+++ b/mozilla/content/base/src/nsPrintEngine.cpp
@@ -2608,7 +2608,8 @@ nsPrintEngine::ReflowPrintObject(nsPrintObject * aPO, PRBool aDoCalcShrink)
   // init it with the DC
   (aPO->mPresContext)->Init(mPrt->mPrintDocDC);
 
-  rv = mDocViewerPrint->CreateStyleSet(aPO->mDocument, &aPO->mStyleSet);
+  rv = mDocViewerPrint->CreateStyleSet(aPO->mDocument,
+                                       getter_Transfers(aPO->mStyleSet));
   NS_ENSURE_SUCCESS(rv, rv);
 
   aPO->mViewManager = do_CreateInstance(kViewManagerCID, &rv);
diff --git a/mozilla/content/base/src/nsPrintObject.h b/mozilla/content/base/src/nsPrintObject.h
index 06cd9638010..d0b732607ed 100644
--- a/mozilla/content/base/src/nsPrintObject.h
+++ b/mozilla/content/base/src/nsPrintObject.h
@@ -81,7 +81,7 @@ public:
 
   PrintObjectType mFrameType;
   nsCOMPtr<nsIPresContext> mPresContext;
-  nsStyleSet              *mStyleSet;
+  nsAutoPtr<nsStyleSet>    mStyleSet;
   nsCOMPtr<nsIPresShell>   mPresShell;
   nsCOMPtr<nsIViewManager> mViewManager;
   nsCOMPtr<nsIWidget>      mWindow;
diff --git a/mozilla/content/base/src/nsRuleNode.cpp b/mozilla/content/base/src/nsRuleNode.cpp
index 54972c6ad12..ccb28d4acfd 100644
--- a/mozilla/content/base/src/nsRuleNode.cpp
+++ b/mozilla/content/base/src/nsRuleNode.cpp
@@ -4358,6 +4358,9 @@ PRBool
 nsRuleNode::Sweep()
 {
   // If we're not marked, then we have to delete ourself.
+  // However, we never allow the root node to GC itself, because nsStyleSet
+  // wants to hold onto the root node and not worry about re-creating a
+  // rule walker if the root node is deleted.
   if (!(mDependentBits & NS_RULE_NODE_GC_MARK) && !IsRoot()) {
     Destroy();
     return PR_TRUE;
diff --git a/mozilla/content/base/src/nsStyleSet.cpp b/mozilla/content/base/src/nsStyleSet.cpp
index 460ac7e944e..f2d7978bdc5 100644
--- a/mozilla/content/base/src/nsStyleSet.cpp
+++ b/mozilla/content/base/src/nsStyleSet.cpp
@@ -55,7 +55,7 @@ nsStyleSet::nsStyleSet()
   : mRuleTree(nsnull),
     mRuleWalker(nsnull),
     mDestroyedCount(0),
-    mBatching(PR_FALSE),
+    mBatching(0),
     mInShutdown(PR_FALSE),
     mDirty(0)
 {
@@ -70,8 +70,10 @@ nsStyleSet::Init(nsIPresContext *aPresContext)
     NS_ENSURE_TRUE(gQuirkURI, NS_ERROR_OUT_OF_MEMORY);
   }
 
-  if (!BuildDefaultStyleData(aPresContext))
-    return NS_ERROR_FAILURE;
+  if (!BuildDefaultStyleData(aPresContext)) {
+    mDefaultStyleData.Destroy(0, aPresContext);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
 
   mRuleTree = nsRuleNode::CreateRootNode(aPresContext);
   if (!mRuleTree) {
@@ -195,10 +197,8 @@ nsStyleSet::ReplaceSheets(sheetType aType,
                           const nsCOMArray<nsIStyleSheet> &aNewSheets)
 {
   mSheets[aType].Clear();
-  for (PRInt32 i = 0; i < aNewSheets.Count(); ++i) {
-    if (!mSheets[aType].AppendObject(aNewSheets.ObjectAt(i)))
-      return NS_ERROR_OUT_OF_MEMORY;
-  }
+  if (!mSheets[aType].AppendObjects(aNewSheets))
+    return NS_ERROR_OUT_OF_MEMORY;
 
   if (!mBatching)
     return GatherRuleProcessors(aType);
@@ -212,7 +212,7 @@ nsStyleSet::ReplaceSheets(sheetType aType,
 nsresult
 nsStyleSet::AddDocStyleSheet(nsIStyleSheet* aSheet, nsIDocument* aDocument)
 {
-  NS_PRECONDITION((nsnull != aSheet) && (nsnull != aDocument), "null arg");
+  NS_PRECONDITION(aSheet && aDocument, "null arg");
   CHECK_APPLICABLE;
 
   nsCOMArray<nsIStyleSheet>& docSheets = mSheets[eDocSheet];
@@ -248,21 +248,26 @@ nsStyleSet::AddDocStyleSheet(nsIStyleSheet* aSheet, nsIDocument* aDocument)
 void
 nsStyleSet::BeginUpdate()
 {
-  mBatching = 1;
+  ++mBatching;
 }
 
 nsresult
 nsStyleSet::EndUpdate()
 {
+  NS_ASSERTION(mBatching > 0, "Unbalanced EndUpdate");
+  if (--mBatching) {
+    // We're not completely done yet.
+    return NS_OK;
+  }
+
   for (int i = 0; i < eSheetTypeCount; ++i) {
-    if (mDirty & 1 << i) {
+    if (mDirty & (1 << i)) {
       nsresult rv = GatherRuleProcessors(i);
       NS_ENSURE_SUCCESS(rv, rv);
     }
   }
 
   mDirty = 0;
-  mBatching = 0;
   return NS_OK;
 }
 
@@ -721,7 +726,7 @@ nsStyleSet::NotifyStyleContextDestroyed(nsIPresContext* aPresContext,
 #endif
       mRuleTree->Sweep();
 
-    NS_ASSERTION(deleted, "Root not must not be gc'd");
+    NS_ASSERTION(!deleted, "Root node must not be gc'd");
   }
 }
 
diff --git a/mozilla/content/base/src/nsStyleSet.h b/mozilla/content/base/src/nsStyleSet.h
index 31cd29049f5..2de04e13a5c 100644
--- a/mozilla/content/base/src/nsStyleSet.h
+++ b/mozilla/content/base/src/nsStyleSet.h
@@ -49,6 +49,10 @@
 
 class nsIURI;
 
+// The style set object is created by the document viewer and ownership is
+// then handed off to the PresShell.  Only the PresShell should delete a
+// style set.
+
 class nsStyleSet
 {
  public:
@@ -156,12 +160,13 @@ class nsStyleSet
   // Free global data at module shutdown
   static void FreeGlobals() { NS_IF_RELEASE(gQuirkURI); }
 
-  // APIs to manipulate the style sheet lists
+  // APIs to manipulate the style sheet lists.
+  // All sheet types are ordered most-significant-first.
   enum sheetType {
     eAgentSheet,
     eUserSheet,
     eDocSheet,
-    eOverrideSheet,  // override sheets are ordered most significant first
+    eOverrideSheet,
     eSheetTypeCount
   };
 
@@ -237,9 +242,10 @@ class nsStyleSet
   PRInt32 mDestroyedCount; // used to batch style context GC
   nsVoidArray mRoots; // style contexts with no parent
 
-  unsigned mBatching : 1;
+  PRUint16 mBatching;
+
   unsigned mInShutdown : 1;
-  unsigned mDirty : 6;  // one dirty bit is used per sheet type
+  unsigned mDirty : 7;  // one dirty bit is used per sheet type
 };
 
 #endif
diff --git a/mozilla/layout/base/nsDocumentViewer.cpp b/mozilla/layout/base/nsDocumentViewer.cpp
index 3e01343df94..ec28baeaf64 100644
--- a/mozilla/layout/base/nsDocumentViewer.cpp
+++ b/mozilla/layout/base/nsDocumentViewer.cpp
@@ -639,8 +639,8 @@ nsresult
 DocumentViewerImpl::InitPresentationStuff(PRBool aDoInitialReflow)
 {
   // Create the style set...
-  nsStyleSet *styleSet;
-  nsresult rv = CreateStyleSet(mDocument, &styleSet);
+  nsAutoPtr<nsStyleSet> styleSet;
+  nsresult rv = CreateStyleSet(mDocument, getter_Transfers(styleSet));
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Now make the shell for the document
@@ -649,6 +649,9 @@ DocumentViewerImpl::InitPresentationStuff(PRBool aDoInitialReflow)
 
   NS_ENSURE_SUCCESS(rv, rv);
 
+  // The pres shell owns the style set now.
+  styleSet.forget();
+
   if (aDoInitialReflow) {
     // Since InitialReflow() will create frames for *all* items
     // that are currently in the document tree, we need to flush
@@ -1191,8 +1194,8 @@ DocumentViewerImpl::SetDOMDocument(nsIDOMDocument *aDocument)
   if (mPresContext) {
     // 3) Create a new style set for the document
 
-    nsStyleSet *styleSet;
-    rv = CreateStyleSet(mDocument, &styleSet);
+    nsAutoPtr<nsStyleSet> styleSet;
+    rv = CreateStyleSet(mDocument, getter_Transfers(styleSet));
     if (NS_FAILED(rv))
       return rv;
 
@@ -1200,6 +1203,9 @@ DocumentViewerImpl::SetDOMDocument(nsIDOMDocument *aDocument)
                              getter_AddRefs(mPresShell));
     NS_ENSURE_SUCCESS(rv, rv);
 
+    // The pres shell owns the style set now.
+    styleSet.forget();
+
     mPresShell->BeginObservingDocument();
 
     // 4) Register the focus listener on the new document
@@ -1594,7 +1600,7 @@ DocumentViewerImpl::CreateStyleSet(nsIDocument* aDocument,
     NS_WARNING("unable to load UA style sheet");
   }
 
-  nsStyleSet *styleSet = new nsStyleSet();
+  nsAutoPtr<nsStyleSet> styleSet(new nsStyleSet());
   if (!styleSet) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -1663,6 +1669,7 @@ DocumentViewerImpl::CreateStyleSet(nsIDocument* aDocument,
 
   styleSet->EndUpdate();
   *aStyleSet = styleSet;
+  styleSet.forget();
   return NS_OK;
 }
 
diff --git a/mozilla/layout/base/nsIPresShell.h b/mozilla/layout/base/nsIPresShell.h
index b24f2e82b5c..db839805d79 100644
--- a/mozilla/layout/base/nsIPresShell.h
+++ b/mozilla/layout/base/nsIPresShell.h
@@ -649,7 +649,7 @@ protected:
   // we must share ownership.
   nsIDocument*              mDocument;      // [STRONG]
   nsIPresContext*           mPresContext;   // [STRONG]
-  nsStyleSet*               mStyleSet;      // [STRONG]
+  nsStyleSet*               mStyleSet;      // [OWNS]
   nsIStyleFrameConstruction* mFrameConstructor; // [STRONG]
   nsIViewManager*           mViewManager;   // [WEAK] docViewer owns it so I don't have to
   nsIFrameManager*          mFrameManager;  // [STRONG]
diff --git a/mozilla/layout/base/nsPresShell.cpp b/mozilla/layout/base/nsPresShell.cpp
index 3b981265bd6..9ccc808178e 100644
--- a/mozilla/layout/base/nsPresShell.cpp
+++ b/mozilla/layout/base/nsPresShell.cpp
@@ -1644,9 +1644,7 @@ PresShell::Init(nsIDocument* aDocument,
   // before creating any frames.
   SetPreferenceStyleRules(PR_FALSE);
 
-  result = nsComponentManager::CreateInstance(kFrameSelectionCID, nsnull,
-                                              NS_GET_IID(nsIFrameSelection),
-                                              getter_AddRefs(mSelection));
+  mSelection = do_CreateInstance(kFrameSelectionCID, &result);
   if (NS_FAILED(result))
     return result;
 
@@ -3541,6 +3539,9 @@ PresShell::BeginUpdate(nsIDocument *aDocument, nsUpdateType aUpdateType)
 #ifdef DEBUG
   mUpdateCount++;
 #endif
+  if (aUpdateType & UPDATE_STYLE)
+    mStyleSet->BeginUpdate();
+
   return NS_OK;
 }
 
@@ -3552,6 +3553,9 @@ PresShell::EndUpdate(nsIDocument *aDocument, nsUpdateType aUpdateType)
   --mUpdateCount;
 #endif
 
+  if (aUpdateType & UPDATE_STYLE)
+    mStyleSet->EndUpdate();
+
   if (mStylesHaveChanged && (aUpdateType & UPDATE_STYLE))
     return ReconstructStyleData();
   
@@ -7097,7 +7101,7 @@ PresShell::VerifyIncrementalReflow()
 
   // Create a new presentation shell to view the document. Use the
   // exact same style information that this document has.
-  nsStyleSet *newSet;
+  nsAutoPtr<nsStyleSet> newSet;
   rv = CloneStyleSet(mStyleSet, &newSet);
   NS_ASSERTION(NS_SUCCEEDED(rv), "failed to clone style set");
   rv = mDocument->CreateShell(cx, vm, newSet, &sh);
diff --git a/mozilla/layout/base/public/nsIPresShell.h b/mozilla/layout/base/public/nsIPresShell.h
index b24f2e82b5c..db839805d79 100644
--- a/mozilla/layout/base/public/nsIPresShell.h
+++ b/mozilla/layout/base/public/nsIPresShell.h
@@ -649,7 +649,7 @@ protected:
   // we must share ownership.
   nsIDocument*              mDocument;      // [STRONG]
   nsIPresContext*           mPresContext;   // [STRONG]
-  nsStyleSet*               mStyleSet;      // [STRONG]
+  nsStyleSet*               mStyleSet;      // [OWNS]
   nsIStyleFrameConstruction* mFrameConstructor; // [STRONG]
   nsIViewManager*           mViewManager;   // [WEAK] docViewer owns it so I don't have to
   nsIFrameManager*          mFrameManager;  // [STRONG]
diff --git a/mozilla/layout/base/public/nsIStyleFrameConstruction.h b/mozilla/layout/base/public/nsIStyleFrameConstruction.h
index 0d56b2cbff4..86579c19f51 100644
--- a/mozilla/layout/base/public/nsIStyleFrameConstruction.h
+++ b/mozilla/layout/base/public/nsIStyleFrameConstruction.h
@@ -57,7 +57,7 @@ class nsILayoutHistoryState;
 
 /** a simple struct (that may someday be expanded)
  * that contains data supplied by the caller to help
- * the style set find a frame for a content node
+ * the frame constructor find a frame for a content node
  */
 struct nsFindFrameHint
 {
diff --git a/mozilla/layout/html/base/src/nsPresShell.cpp b/mozilla/layout/html/base/src/nsPresShell.cpp
index 3b981265bd6..9ccc808178e 100644
--- a/mozilla/layout/html/base/src/nsPresShell.cpp
+++ b/mozilla/layout/html/base/src/nsPresShell.cpp
@@ -1644,9 +1644,7 @@ PresShell::Init(nsIDocument* aDocument,
   // before creating any frames.
   SetPreferenceStyleRules(PR_FALSE);
 
-  result = nsComponentManager::CreateInstance(kFrameSelectionCID, nsnull,
-                                              NS_GET_IID(nsIFrameSelection),
-                                              getter_AddRefs(mSelection));
+  mSelection = do_CreateInstance(kFrameSelectionCID, &result);
   if (NS_FAILED(result))
     return result;
 
@@ -3541,6 +3539,9 @@ PresShell::BeginUpdate(nsIDocument *aDocument, nsUpdateType aUpdateType)
 #ifdef DEBUG
   mUpdateCount++;
 #endif
+  if (aUpdateType & UPDATE_STYLE)
+    mStyleSet->BeginUpdate();
+
   return NS_OK;
 }
 
@@ -3552,6 +3553,9 @@ PresShell::EndUpdate(nsIDocument *aDocument, nsUpdateType aUpdateType)
   --mUpdateCount;
 #endif
 
+  if (aUpdateType & UPDATE_STYLE)
+    mStyleSet->EndUpdate();
+
   if (mStylesHaveChanged && (aUpdateType & UPDATE_STYLE))
     return ReconstructStyleData();
   
@@ -7097,7 +7101,7 @@ PresShell::VerifyIncrementalReflow()
 
   // Create a new presentation shell to view the document. Use the
   // exact same style information that this document has.
-  nsStyleSet *newSet;
+  nsAutoPtr<nsStyleSet> newSet;
   rv = CloneStyleSet(mStyleSet, &newSet);
   NS_ASSERTION(NS_SUCCEEDED(rv), "failed to clone style set");
   rv = mDocument->CreateShell(cx, vm, newSet, &sh);
diff --git a/mozilla/layout/printing/nsPrintEngine.cpp b/mozilla/layout/printing/nsPrintEngine.cpp
index 151e4cc9e08..a4c8dc21387 100644
--- a/mozilla/layout/printing/nsPrintEngine.cpp
+++ b/mozilla/layout/printing/nsPrintEngine.cpp
@@ -2608,7 +2608,8 @@ nsPrintEngine::ReflowPrintObject(nsPrintObject * aPO, PRBool aDoCalcShrink)
   // init it with the DC
   (aPO->mPresContext)->Init(mPrt->mPrintDocDC);
 
-  rv = mDocViewerPrint->CreateStyleSet(aPO->mDocument, &aPO->mStyleSet);
+  rv = mDocViewerPrint->CreateStyleSet(aPO->mDocument,
+                                       getter_Transfers(aPO->mStyleSet));
   NS_ENSURE_SUCCESS(rv, rv);
 
   aPO->mViewManager = do_CreateInstance(kViewManagerCID, &rv);
diff --git a/mozilla/layout/printing/nsPrintObject.h b/mozilla/layout/printing/nsPrintObject.h
index 06cd9638010..d0b732607ed 100644
--- a/mozilla/layout/printing/nsPrintObject.h
+++ b/mozilla/layout/printing/nsPrintObject.h
@@ -81,7 +81,7 @@ public:
 
   PrintObjectType mFrameType;
   nsCOMPtr<nsIPresContext> mPresContext;
-  nsStyleSet              *mStyleSet;
+  nsAutoPtr<nsStyleSet>    mStyleSet;
   nsCOMPtr<nsIPresShell>   mPresShell;
   nsCOMPtr<nsIViewManager> mViewManager;
   nsCOMPtr<nsIWidget>      mWindow;
diff --git a/mozilla/layout/style/nsRuleNode.cpp b/mozilla/layout/style/nsRuleNode.cpp
index 54972c6ad12..ccb28d4acfd 100644
--- a/mozilla/layout/style/nsRuleNode.cpp
+++ b/mozilla/layout/style/nsRuleNode.cpp
@@ -4358,6 +4358,9 @@ PRBool
 nsRuleNode::Sweep()
 {
   // If we're not marked, then we have to delete ourself.
+  // However, we never allow the root node to GC itself, because nsStyleSet
+  // wants to hold onto the root node and not worry about re-creating a
+  // rule walker if the root node is deleted.
   if (!(mDependentBits & NS_RULE_NODE_GC_MARK) && !IsRoot()) {
     Destroy();
     return PR_TRUE;
diff --git a/mozilla/layout/style/nsStyleSet.cpp b/mozilla/layout/style/nsStyleSet.cpp
index 460ac7e944e..f2d7978bdc5 100644
--- a/mozilla/layout/style/nsStyleSet.cpp
+++ b/mozilla/layout/style/nsStyleSet.cpp
@@ -55,7 +55,7 @@ nsStyleSet::nsStyleSet()
   : mRuleTree(nsnull),
     mRuleWalker(nsnull),
     mDestroyedCount(0),
-    mBatching(PR_FALSE),
+    mBatching(0),
     mInShutdown(PR_FALSE),
     mDirty(0)
 {
@@ -70,8 +70,10 @@ nsStyleSet::Init(nsIPresContext *aPresContext)
     NS_ENSURE_TRUE(gQuirkURI, NS_ERROR_OUT_OF_MEMORY);
   }
 
-  if (!BuildDefaultStyleData(aPresContext))
-    return NS_ERROR_FAILURE;
+  if (!BuildDefaultStyleData(aPresContext)) {
+    mDefaultStyleData.Destroy(0, aPresContext);
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
 
   mRuleTree = nsRuleNode::CreateRootNode(aPresContext);
   if (!mRuleTree) {
@@ -195,10 +197,8 @@ nsStyleSet::ReplaceSheets(sheetType aType,
                           const nsCOMArray<nsIStyleSheet> &aNewSheets)
 {
   mSheets[aType].Clear();
-  for (PRInt32 i = 0; i < aNewSheets.Count(); ++i) {
-    if (!mSheets[aType].AppendObject(aNewSheets.ObjectAt(i)))
-      return NS_ERROR_OUT_OF_MEMORY;
-  }
+  if (!mSheets[aType].AppendObjects(aNewSheets))
+    return NS_ERROR_OUT_OF_MEMORY;
 
   if (!mBatching)
     return GatherRuleProcessors(aType);
@@ -212,7 +212,7 @@ nsStyleSet::ReplaceSheets(sheetType aType,
 nsresult
 nsStyleSet::AddDocStyleSheet(nsIStyleSheet* aSheet, nsIDocument* aDocument)
 {
-  NS_PRECONDITION((nsnull != aSheet) && (nsnull != aDocument), "null arg");
+  NS_PRECONDITION(aSheet && aDocument, "null arg");
   CHECK_APPLICABLE;
 
   nsCOMArray<nsIStyleSheet>& docSheets = mSheets[eDocSheet];
@@ -248,21 +248,26 @@ nsStyleSet::AddDocStyleSheet(nsIStyleSheet* aSheet, nsIDocument* aDocument)
 void
 nsStyleSet::BeginUpdate()
 {
-  mBatching = 1;
+  ++mBatching;
 }
 
 nsresult
 nsStyleSet::EndUpdate()
 {
+  NS_ASSERTION(mBatching > 0, "Unbalanced EndUpdate");
+  if (--mBatching) {
+    // We're not completely done yet.
+    return NS_OK;
+  }
+
   for (int i = 0; i < eSheetTypeCount; ++i) {
-    if (mDirty & 1 << i) {
+    if (mDirty & (1 << i)) {
       nsresult rv = GatherRuleProcessors(i);
       NS_ENSURE_SUCCESS(rv, rv);
     }
   }
 
   mDirty = 0;
-  mBatching = 0;
   return NS_OK;
 }
 
@@ -721,7 +726,7 @@ nsStyleSet::NotifyStyleContextDestroyed(nsIPresContext* aPresContext,
 #endif
       mRuleTree->Sweep();
 
-    NS_ASSERTION(deleted, "Root not must not be gc'd");
+    NS_ASSERTION(!deleted, "Root node must not be gc'd");
   }
 }
 
diff --git a/mozilla/layout/style/nsStyleSet.h b/mozilla/layout/style/nsStyleSet.h
index 31cd29049f5..2de04e13a5c 100644
--- a/mozilla/layout/style/nsStyleSet.h
+++ b/mozilla/layout/style/nsStyleSet.h
@@ -49,6 +49,10 @@
 
 class nsIURI;
 
+// The style set object is created by the document viewer and ownership is
+// then handed off to the PresShell.  Only the PresShell should delete a
+// style set.
+
 class nsStyleSet
 {
  public:
@@ -156,12 +160,13 @@ class nsStyleSet
   // Free global data at module shutdown
   static void FreeGlobals() { NS_IF_RELEASE(gQuirkURI); }
 
-  // APIs to manipulate the style sheet lists
+  // APIs to manipulate the style sheet lists.
+  // All sheet types are ordered most-significant-first.
   enum sheetType {
     eAgentSheet,
     eUserSheet,
     eDocSheet,
-    eOverrideSheet,  // override sheets are ordered most significant first
+    eOverrideSheet,
     eSheetTypeCount
   };
 
@@ -237,9 +242,10 @@ class nsStyleSet
   PRInt32 mDestroyedCount; // used to batch style context GC
   nsVoidArray mRoots; // style contexts with no parent
 
-  unsigned mBatching : 1;
+  PRUint16 mBatching;
+
   unsigned mInShutdown : 1;
-  unsigned mDirty : 6;  // one dirty bit is used per sheet type
+  unsigned mDirty : 7;  // one dirty bit is used per sheet type
 };
 
 #endif