Just use instanceof Ci.nsIDOMElement for Utils.isDOMElement for bug 582023.

browser/base/content/tabview/modules/utils.jsm

@@ -576,7 +576,7 @@ let Utils = {
   // Function: isDOMElement
   // Returns true if the given object is a DOM element.
   isDOMElement: function(object) {
-    return (object && typeof(object.nodeType) != 'undefined' ? true : false);
+    return object instanceof Ci.nsIDOMElement;
   },
 
   // ----------