Well, It looks like the converter is somehow broken.
If i take an hello world script with this content:
// ==UserScript==
// @name Webmonkey's Hello World
// @namespace http://www.webmonkey.com
// @description A basic example of Greasemonkey that causes an alert at each page load.
// @include *
// ==/UserScript==
alert('Monkey sez... "Hello World!"');
The error is still there. So i don't suspect that your code is the problem, more the compiler.
I've never created an XPI by myself, but i think that you should try it by hand and see if that works. Perhaps will this problem be fixed in the future ( watch his github page for updates )