onToolbarButtonCommand: function(e) {
     var prefs = Components.classes["@mozilla.org/preferences-service;1"].
          getService(Components.interfaces.nsIPrefBranch);
     if(prefs.getBoolPref("extensions.RSWorldLoad.showPopup")){
          //Stop Dropdown
          window.open("chrome://RSWorldLoad/content/PageSelect.xul", "PageSelect", "chrome,resizable=yes,scrollbars=yes,alwaysRaised=yes");
     }else{
          //allow dropdown
     }
  },