add:  var aus = Components.classes["@mozilla.org/updates/update-service;1"]. getService(Components.interfaces.nsIApplicationUpdateService); var checkNowButton = document.getElementById("checkNowButton"); checkNowButton.disabled = !aus.canUpdate;  
context:   updateAppUpdateUI: function ()  {    var preference = document.getElementById("app.update.enabled");    document.getElementById("enableAutoInstall").disabled = !preference.value;    this.updateAutoInstallUI();    return undefined;  },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/5b9489e9046633a4e8287838684d61e69a791c65/advanced.js/buggy/browser/components/preferences/advanced.js