rem: this.mPrefs.removeObserver(aDomain, aFunction); 
add: var pbi = XPCU.QI(this.mPrefs, "nsIPrefBranchInternal"); if (pbi) pbi.removeObserver(aDomain, aFunction); 
context:   removeObserver: function(aDomain, aFunction)  {    if (!this.mPrefs) this.init();    this.mPrefs.removeObserver(aDomain, aFunction);  },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/3edc819898ac6c062c72851e4d1ae1bc218b8c85/PrefUtils.js/buggy/extensions/inspector/resources/content/jsutil/system/PrefUtils.js