rem: var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranchInternal"); 
add: var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranch2"); 
context:   addObserver: function(aDomain, aFunction)  {    if (!this.mPrefs) this.init();    var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranchInternal");    if (pbi)      pbi.addObserver(aDomain, aFunction, false);  },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/f72d2b7f36d9d7bbb6c4161b5eba6b9806b00c03/PrefUtils.js/buggy/extensions/inspector/resources/content/jsutil/system/PrefUtils.js