diff --git a/content/html/document/src/nsHTMLDocument.h b/content/html/document/src/nsHTMLDocument.h
index cf7a1b17fa1e..05f9480eb37f 100644
--- a/content/html/document/src/nsHTMLDocument.h
+++ b/content/html/document/src/nsHTMLDocument.h
@@ -79,9 +79,6 @@ class nsHTMLDocument : public nsDocument,
     return mWriteLevel != PRUint32(0);
   }
 
-  virtual bool GetIsFrameset() { return mIsFrameset; }
-  virtual void SetIsFrameset(bool aFrameset) { mIsFrameset = aFrameset; }
-
   virtual NS_HIDDEN_(nsContentList*) GetForms();
  
   virtual NS_HIDDEN_(nsContentList*) GetFormControls();
@@ -253,8 +250,6 @@ class nsHTMLDocument : public nsDocument,
   // Load flags of the document's channel
   PRUint32 mLoadFlags;
 
-  bool mIsFrameset;
-
   bool mTooDeepWriteRecursion;
 
   bool mDisableDocWrite;
diff --git a/content/html/document/src/nsIHTMLDocument.h b/content/html/document/src/nsIHTMLDocument.h
index c6f4be4f6535..a11541892455 100644
--- a/content/html/document/src/nsIHTMLDocument.h
+++ b/content/html/document/src/nsIHTMLDocument.h
@@ -17,8 +17,8 @@ class nsContentList;
 class nsWrapperCache;
 
 #define NS_IHTMLDOCUMENT_IID \
-{ 0xa921276f, 0x5e70, 0x42e0, \
-  { 0xb8, 0x36, 0x7e, 0x6a, 0xb8, 0x30, 0xb3, 0xc0 } }
+{ 0xcf814492, 0x303c, 0x4718, \
+  { 0x9a, 0x3e, 0x39, 0xbc, 0xd5, 0x2c, 0x10, 0xdb } }
 
 /**
  * HTML document extensions to nsIDocument.
@@ -58,9 +58,6 @@ class nsIHTMLDocument : public nsISupports
   
   virtual bool IsWriting() = 0;
 
-  virtual bool GetIsFrameset() = 0;
-  virtual void SetIsFrameset(bool aFrameset) = 0;
-
   /**
    * Get the list of form elements in the document.
    */
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index d8421ec58bf4..ba8481df801f 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -726,13 +726,6 @@ DocumentViewerImpl::InitPresentationStuff(bool aDoInitialReflow)
   mPresContext->SetMinFontSize(mMinFontSize);
 
   if (aDoInitialReflow) {
-    nsCOMPtr<nsIHTMLDocument> htmlDoc = do_QueryInterface(mDocument);
-    if (htmlDoc) {
-      nsCOMPtr<nsIDOMHTMLFrameSetElement> frameset =
-        do_QueryInterface(mDocument->GetRootElement());
-      htmlDoc->SetIsFrameset(frameset != nsnull);
-    }
-
     nsCOMPtr<nsIPresShell> shellGrip = mPresShell;
     // Initial reflow
     mPresShell->InitialReflow(width, height);
diff --git a/parser/html/nsHtml5TreeOperation.cpp b/parser/html/nsHtml5TreeOperation.cpp
index ab09563f0415..750d83b94fbd 100644
--- a/parser/html/nsHtml5TreeOperation.cpp
+++ b/parser/html/nsHtml5TreeOperation.cpp
@@ -392,14 +392,6 @@ nsHtml5TreeOperation::Perform(nsHtml5TreeOpExecutor* aBuilder,
           newContent->AppendChildTo(optionElt, false);
           newContent->DoneAddingChildren(false);
         }
-      } else if (name == nsHtml5Atoms::frameset && ns == kNameSpaceID_XHTML) {
-        nsIDocument* doc = aBuilder->GetDocument();
-        nsCOMPtr<nsIHTMLDocument> htmlDocument = do_QueryInterface(doc);
-        if (htmlDocument) {
-          // It seems harmless to call this multiple times, since this 
-          // is a simple field setter
-          htmlDocument->SetIsFrameset(true);
-        }
       }
 
       if (!attributes) {