rem: var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranchInternal"); 
add: var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranch2"); 
context:   removeObserver: function(aDomain, aFunction)  {    if (!this.mPrefs) this.init();    var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranchInternal");    if (pbi)      pbi.removeObserver(aDomain, aFunction);  },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/c09049633a1ada8202548fb4d74fffed2cf79763/PrefUtils.js/buggy/extensions/inspector/resources/content/jsutil/system/PrefUtils.js