rem: document.documentElement.getButton("next").disabled = !enabled; 
add: this.updateNextButton(); 
context:   toggleXPInstallEnable: function(aEvent)  {    var enabled = aEvent.target.checked;    gUpdateWizard.xpinstallEnabled = enabled;    var pref = Components.classes["@mozilla.org/preferences-service;1"]                         .getService(Components.interfaces.nsIPrefBranch);    pref.setBoolPref(PREF_XPINSTALL_ENABLED, enabled);    document.documentElement.getButton("next").disabled = !enabled;  },
meta: 5459	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5459/f6eaa90736e7beb3ceaf8a1ef7cf2f642cf43cdf/update.js/clean/toolkit/mozapps/extensions/content/update.js