diff --git a/mozilla/layout/style/html.css b/mozilla/layout/style/html.css
index 569c92d6758..c5cd9cbfed7 100644
--- a/mozilla/layout/style/html.css
+++ b/mozilla/layout/style/html.css
@@ -252,6 +252,13 @@ th {
   padding: 1px;
 }
 
+tr > form:-moz-is-html, tbody > form:-moz-is-html,
+thead > form:-moz-is-html, tfoot > form:-moz-is-html,
+table > form:-moz-is-html {
+  /* Important: don't show these forms in HTML */
+  display: none !important;
+}
+
 /* inlines */
 
 q:before {
diff --git a/mozilla/layout/style/nsCSSPseudoClassList.h b/mozilla/layout/style/nsCSSPseudoClassList.h
index aa44821b531..17fe8fb4608 100644
--- a/mozilla/layout/style/nsCSSPseudoClassList.h
+++ b/mozilla/layout/style/nsCSSPseudoClassList.h
@@ -76,6 +76,9 @@ CSS_PSEUDO_CLASS(lastChild, ":last-child")
 CSS_PSEUDO_CLASS(lastNode, ":-moz-last-node")
 CSS_PSEUDO_CLASS(onlyChild, ":only-child")
 
+// Match nodes that are HTML but not XHTML
+CSS_PSEUDO_CLASS(mozIsHTML, ":-moz-is-html")
+
 // CSS 3 UI
 // http://www.w3.org/TR/2004/CR-css3-ui-20040511/#pseudo-classes
 CSS_PSEUDO_CLASS(required, ":required")
diff --git a/mozilla/layout/style/nsCSSStyleSheet.cpp b/mozilla/layout/style/nsCSSStyleSheet.cpp
index fc999a2916a..326eb74574a 100644
--- a/mozilla/layout/style/nsCSSStyleSheet.cpp
+++ b/mozilla/layout/style/nsCSSStyleSheet.cpp
@@ -3158,6 +3158,12 @@ static PRBool SelectorMatches(RuleProcessorData &data,
     else if (nsCSSPseudoClasses::mozReadWrite == pseudoClass->mAtom) {
       result = STATE_CHECK(NS_EVENT_STATE_MOZ_READWRITE);
     }
+    else if (nsCSSPseudoClasses::mozIsHTML == pseudoClass->mAtom) {
+      result =
+        (data.mIsHTMLContent &&
+         data.mContent->GetNameSpaceID() == kNameSpaceID_None) ? localTrue :
+                                                                 localFalse;
+    }
     else {
       NS_ERROR("CSS parser parsed a pseudo-class that we do not handle");
       result = PR_FALSE;  // unknown pseudo class
diff --git a/mozilla/layout/style/nsHTMLStyleSheet.cpp b/mozilla/layout/style/nsHTMLStyleSheet.cpp
index b6048ad9455..b9ec9e509a6 100644
--- a/mozilla/layout/style/nsHTMLStyleSheet.cpp
+++ b/mozilla/layout/style/nsHTMLStyleSheet.cpp
@@ -85,28 +85,7 @@ nsHTMLStyleSheet::HTMLColorRule::List(FILE* out, PRInt32 aIndent) const
 }
 #endif
 
-
-NS_IMPL_ISUPPORTS1(nsHTMLStyleSheet::TableFormRule, nsIStyleRule)
-
-NS_IMETHODIMP
-nsHTMLStyleSheet::TableFormRule::MapRuleInfoInto(nsRuleData* aRuleData)
-{
-  if (aRuleData->mSID == eStyleStruct_Display &&
-      aRuleData->mDisplayData->mDisplay.GetUnit() == eCSSUnit_Null) {
-    nsCSSValue none(NS_STYLE_DISPLAY_NONE, eCSSUnit_Enumerated);
-    aRuleData->mDisplayData->mDisplay = none;
-  }
-  return NS_OK;
-}
-
-#ifdef DEBUG
-NS_IMETHODIMP
-nsHTMLStyleSheet::TableFormRule::List(FILE* out, PRInt32 aIndent) const
-{
-  return NS_OK;
-}
-#endif
-
+ 
 NS_IMPL_ISUPPORTS1(nsHTMLStyleSheet::GenericTableRule, nsIStyleRule)
 
 NS_IMETHODIMP
@@ -347,8 +326,7 @@ nsHTMLStyleSheet::nsHTMLStyleSheet(void)
     mLinkRule(nsnull),
     mVisitedRule(nsnull),
     mActiveRule(nsnull),
-    mDocumentColorRule(nsnull),
-    mTableFormRule(nsnull)
+    mDocumentColorRule(nsnull)
 {
   mMappedAttrTable.ops = nsnull;
 }
@@ -380,11 +358,6 @@ nsHTMLStyleSheet::Init()
   if (!mTableTHRule)
     return NS_ERROR_OUT_OF_MEMORY;
   NS_ADDREF(mTableTHRule);
-
-  mTableFormRule = new TableFormRule();
-  if (!mTableFormRule)
-    return NS_ERROR_OUT_OF_MEMORY;
-  NS_ADDREF(mTableFormRule);
   return NS_OK;
 }
 
@@ -396,7 +369,6 @@ nsHTMLStyleSheet::~nsHTMLStyleSheet()
   NS_IF_RELEASE(mVisitedRule);
   NS_IF_RELEASE(mActiveRule);
   NS_IF_RELEASE(mDocumentColorRule);
-  NS_IF_RELEASE(mTableFormRule);
   NS_IF_RELEASE(mTableTbodyRule);
   NS_IF_RELEASE(mTableRowRule);
   NS_IF_RELEASE(mTableColgroupRule);
@@ -494,26 +466,6 @@ nsHTMLStyleSheet::RulesMatching(ElementRuleProcessorData* aData)
             ruleWalker->Forward(mDocumentColorRule);
         }
       }
-      else if (tag == nsHTMLAtoms::form) {
-        // suppress in html documents empty forms inside tables,
-        // they have been used as a hack
-        // to avoid the form top and bottom margin
-        nsIDocument* doc   = styledContent->GetOwnerDoc();
-        nsIContent* parent = styledContent->GetParent();
-        if (!styledContent->GetChildCount() &&  // form is empty
-            doc && !doc->IsCaseSensitive() && // document is not XHTML
-            parent && parent->IsContentOfType(nsIContent::eHTML)) { 
-            // parent is HTML
-          nsIAtom* parentTag = parent->Tag();
-          if ((nsHTMLAtoms::table == parentTag) ||
-             (nsHTMLAtoms::tr == parentTag) ||
-              (nsHTMLAtoms::tbody == parentTag) ||
-              (nsHTMLAtoms::thead == parentTag) ||
-              (nsHTMLAtoms::tfoot == parentTag)) {
-            ruleWalker->Forward(mTableFormRule);
-          }
-        }
-      }
     } // end html element
 
     // just get the style rules from the content
@@ -704,7 +656,6 @@ nsHTMLStyleSheet::Reset(nsIURI* aURL)
   NS_IF_RELEASE(mVisitedRule);
   NS_IF_RELEASE(mActiveRule);
   NS_IF_RELEASE(mDocumentColorRule);
-  NS_IF_RELEASE(mTableFormRule);
 
   if (mMappedAttrTable.ops) {
     PL_DHashTableFinish(&mMappedAttrTable);
diff --git a/mozilla/layout/style/nsHTMLStyleSheet.h b/mozilla/layout/style/nsHTMLStyleSheet.h
index f6f599419ab..8e109f361f1 100644
--- a/mozilla/layout/style/nsHTMLStyleSheet.h
+++ b/mozilla/layout/style/nsHTMLStyleSheet.h
@@ -119,23 +119,6 @@ private:
   };
 
 
-  // this rule supresses forms inside table tags in html
-  class TableFormRule;
-  friend class TableFormRule;
-  class TableFormRule: public nsIStyleRule {
-  public:
-    TableFormRule() {}
-    
-     NS_DECL_ISUPPORTS
-
-    // nsIStyleRule interface
-    NS_IMETHOD MapRuleInfoInto(nsRuleData* aRuleData);
-  #ifdef DEBUG
-    NS_IMETHOD List(FILE* out = stdout, PRInt32 aIndent = 0) const;
-  #endif
-  };
-
-
   class GenericTableRule;
   friend class GenericTableRule;
   class GenericTableRule: public nsIStyleRule {
@@ -208,7 +191,6 @@ private:
   HTMLColorRule*       mVisitedRule;
   HTMLColorRule*       mActiveRule;
   HTMLColorRule*       mDocumentColorRule;
-  TableFormRule*       mTableFormRule;
   TableTbodyRule*      mTableTbodyRule;
   TableRowRule*        mTableRowRule;
   TableColgroupRule*   mTableColgroupRule;