Bug 706746 - Don't try to close the Inspector's "Leaving this page" notification bar twice. r=msucan

browser/devtools/highlighter/inspector.jsm

@@ -2220,7 +2220,9 @@ InspectorProgressListener.prototype = {
             aRequest.resume();
             aRequest = null;
             this.IUI.closeInspectorUI();
+            return true;
           }
+          return false;
         }.bind(this),
       },
       {