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: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/8aff9aeb07c9c959fbac47c4af798767bb55a87c/pref-manager.js/buggy/extensions/irc/js/lib/pref-manager.js