--- a/content/base/public/nsIContent.h
+++ b/content/base/public/nsIContent.h
@@ -60,16 +60,17 @@ public:
   // If you're using the external API, the only thing you can know about
   // nsIContent is that it exists with an IID
 
   nsIContent(already_AddRefed<nsINodeInfo> aNodeInfo)
     : nsINode(aNodeInfo)
   {
     NS_ASSERTION(mNodeInfo,
                  "No nsINodeInfo passed to nsIContent, PREPARE TO CRASH!!!");
+    SetNodeIsContent();
   }
 #endif // MOZILLA_INTERNAL_API
 
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_ICONTENT_IID)
 
   /**
    * Bind this content node to a tree.  If this method throws, the caller must
    * call UnbindFromTree() on the node.  In the typical case of a node being

--- a/content/base/public/nsINode.h
+++ b/content/base/public/nsINode.h
@@ -370,23 +370,16 @@ public:
 
   /**
    * Return this node as an Element.  Should only be used for nodes
    * for which IsElement() is true.  This is defined inline in Element.h.
    */
   mozilla::dom::Element* AsElement();
 
   /**
-   * Return whether the node is a content node
-   */
-  bool IsContent() const {
-    return IsNodeOfType(eCONTENT);
-  }
-
-  /**
    * Return this node as nsIContent.  Should only be used for nodes for which
    * IsContent() is true.  This is defined inline in nsIContent.h.
    */
   nsIContent* AsContent();
 
   virtual nsIDOMNode* AsDOMNode() = 0;
 
   /**
@@ -1277,16 +1270,18 @@ private:
     // Set if the node has an explicit base URI stored
     NodeHasExplicitBaseURI,
     // Set if the element has some style states locked
     ElementHasLockedStyleStates,
     // Set if element has pointer locked
     ElementHasPointerLock,
     // Set if the node may have DOMMutationObserver attached to it.
     NodeMayHaveDOMMutationObserver,
+    // Set if node is Content
+    NodeIsContent,
     // Guard value
     BooleanFlagCount
   };
 
   void SetBoolFlag(BooleanFlag name, bool value) {
     PR_STATIC_ASSERT(BooleanFlagCount <= 8*sizeof(mBoolFlags));
     mBoolFlags = (mBoolFlags & ~(1 << name)) | (value << name);
   }
@@ -1306,16 +1301,17 @@ private:
     return mBoolFlags & (1 << name);
   }
 
 public:
   bool HasRenderingObservers() const
     { return GetBoolFlag(NodeHasRenderingObservers); }
   void SetHasRenderingObservers(bool aValue)
     { SetBoolFlag(NodeHasRenderingObservers, aValue); }
+  bool IsContent() const { return GetBoolFlag(NodeIsContent); }
   bool HasID() const { return GetBoolFlag(ElementHasID); }
   bool MayHaveStyle() const { return GetBoolFlag(ElementMayHaveStyle); }
   bool HasName() const { return GetBoolFlag(ElementHasName); }
   bool MayHaveContentEditableAttr() const
     { return GetBoolFlag(ElementMayHaveContentEditableAttr); }
   bool IsCommonAncestorForRangeInSelection() const
     { return GetBoolFlag(NodeIsCommonAncestorForRangeInSelection); }
   void SetCommonAncestorForRangeInSelection()
@@ -1344,16 +1340,17 @@ public:
     { SetBoolFlag(NodeMayHaveDOMMutationObserver, true); }
   bool HasListenerManager() { return HasFlag(NODE_HAS_LISTENERMANAGER); }
   bool HasPointerLock() const { return GetBoolFlag(ElementHasPointerLock); }
   void SetPointerLock() { SetBoolFlag(ElementHasPointerLock); }
   void ClearPointerLock() { ClearBoolFlag(ElementHasPointerLock); }
 protected:
   void SetParentIsContent(bool aValue) { SetBoolFlag(ParentIsContent, aValue); }
   void SetInDocument() { SetBoolFlag(IsInDocument); }
+  void SetNodeIsContent() { SetBoolFlag(NodeIsContent); }
   void ClearInDocument() { ClearBoolFlag(IsInDocument); }
   void SetIsElement() { SetBoolFlag(NodeIsElement); }
   void ClearIsElement() { ClearBoolFlag(NodeIsElement); }
   void SetHasID() { SetBoolFlag(ElementHasID); }
   void ClearHasID() { ClearBoolFlag(ElementHasID); }
   void SetMayHaveStyle() { SetBoolFlag(ElementMayHaveStyle); }
   void SetHasName() { SetBoolFlag(ElementHasName); }
   void ClearHasName() { ClearBoolFlag(ElementHasName); }