rem: var pbi = pref.QueryInterface(Components.interfaces.nsIPrefBranchInternal); 
add: var pbi = pref.QueryInterface(Components.interfaces.nsIPrefBranch2); 
context: function removePrefListener(observer){  try {    var pbi = pref.QueryInterface(Components.interfaces.nsIPrefBranchInternal);    pbi.removeObserver(observer.domain, observer);  } catch(ex) {    dump("Failed to remove pref observer: " + ex + "\n");  }}
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/4b68fa447a8983137138e2d20be274a6c51fc137/navigator.js/buggy/xpfe/browser/resources/content/navigator.js