  observe: function (aSubject, aTopic, aData)  {    if (aTopic == "shell:desktop-background-changed") {      var setDesktopBackground = document.getElementById("setDesktopBackground");      setDesktopBackground.hidden = true;            var showDesktopPreferences = document.getElementById("showDesktopPreferences");      showDesktopPreferences.hidden = false;      var os = Components.classes["@mozilla.org/observer-service;1"]                         .getService(Components.interfaces.nsIObserverService);      os.removeObserver(this, "shell:desktop-background-changed");    }  },
5872	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/5872/f932fa378f3c869b419186ccf62d7c6935c66364/setDesktopBackground.js/buggy/browser/components/shell/content/setDesktopBackground.js