add: if (!aFocusedWindow) return false;  
context: function isContentFrame(aFocusedWindow){  var focusedTop = Components.lookupMethod(aFocusedWindow, 'top')                             .call(aFocusedWindow);  return (focusedTop == window.content);}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/5bbf5e01e06fdd18e6da59e6b88dcd5d7c1ac0f8/contentAreaUtils.js/buggy/suite/common/contentAreaUtils.js