XUL is an XML language which uses javascript. All the Mozilla programs interfaces are build with it.
It has the great advantage of being multi OS, and extensions have easy ways to modify menus, ...
It has the big disadvantage to be long to execute, and more sensible to security problems than the way used by K-Meleon.
A+
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Web:
http://jujuland.pagesperso-orange.fr/
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc