add: if (!aFocusedWindow) return false;  
context: function isContentFrame(aFocusedWindow){  var focusedTop = Components.lookupMethod(aFocusedWindow, 'top')                             .call(aFocusedWindow);  return (focusedTop == window.content);}
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/512f3013d6d7db8257977abe38df31085a61d42e/contentAreaUtils.js/buggy/xpfe/communicator/resources/content/contentAreaUtils.js