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/2006/9421/607ef1c5b6859709dc1f0d9c28960b8aec7c4c3a/browser.js/clean/browser/base/content/browser.js