--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -2601,27 +2601,29 @@ function getMarkupDocumentViewer()
 }
 
 /**
  * Content area tooltip.
  * XXX - this must move into XBL binding/equiv! Do not want to pollute
  *       browser.js with functionality that can be encapsulated into
  *       browser widget. TEMPORARY!
  *
- * NOTE: Any changes to this routine need to be mirrored in ChromeListener::FindTitleText()
+ * NOTE: Any changes to this routine need to be mirrored in DefaultTooltipTextProvider::GetNodeText()
  *       (located in mozilla/embedding/browser/webBrowser/nsDocShellTreeOwner.cpp)
  *       which performs the same function, but for embedded clients that
  *       don't use a XUL/JS layer. It is important that the logic of
  *       these two routines be kept more or less in sync.
  *       (pinkerton)
  **/
 function FillInHTMLTooltip(tipElement)
 {
   var retVal = false;
-  if (tipElement.namespaceURI == "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul")
+  // Don't show the tooltip if the tooltip node is a XUL element or a document.
+  if (tipElement.namespaceURI == "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" ||
+      !tipElement.ownerDocument)
     return retVal;
 
   const XLinkNS = "http://www.w3.org/1999/xlink";
 
 
   var titleText = null;
   var XLinkTitleText = null;
   var SVGTitleText = null;