rem: this.stopCmd.removeAttribute("disabled"); 
add: if (this.stopCmd) this.stopCmd.removeAttribute("disabled"); 
context:   _startMeteors : function()    {      this.ensureStatusFields();      this.meteorsSpinning = true;      this.startTimeoutID = null;      // Turn progress meter on.      this.statusBar.setAttribute("mode","undetermined");      // turn throbber on      this.throbber.setAttribute("busy", true);      //turn on stop button and menu    this.stopCmd.removeAttribute("disabled");    },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/26e84c6e9330b25a72f791d7f81880f785be948a/mailWindow.js/clean/mailnews/base/resources/content/mailWindow.js