java
keyword is not available here. There is one trick that allow you to get reference on
java
variable from XPCOM:const Cc = Components.classes;
const Ci = Components.interfaces;
var java = Cc["@mozilla.org/appshell/window-mediator;1"].
getService(Ci.nsIWindowMediator).
getMostRecentWindow("navigator:browser").java;
Very simple, but not very obvious.