add:  if (!(prefName in this.prefRecords)) return;  
context: function pm_prefchanged(prefName, realValue, oldValue){    for (var i = 0; i < this.observers.length; i++)        this.observers[i].onPrefChanged(prefName, realValue, oldValue);}
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/5d8dd9cbddbd6575e8a3783f74cadff144910d59/pref-manager.js/clean/extensions/irc/js/lib/pref-manager.js