A new post on the PHP-GTK Community website has pointed out the beta release of a PHP-GTK tool for parsing XUL - Gul 2.0.
2 years after begining, I'm happy to announce you the "Beta" release of the Gul 2.0 project, the XUL parser for PHP GTK (97% released). I have to do lot of things, but i think it looks like something.
You can find out more information about the project on the Gul project page over on the redsoft.net domain (including the downloads).