XUL: eXtensible User-interface Language - XUL is Mozilla's XML-based User interface Language that lets you build feature-rich cross platform applications that can run connected or disconnected from the Internet (from "The Joy of XUL"). Read on for links to sample XUL applications you can try in Mozilla, and tutorials and resources for developing your own XUL applications. [Ed Tech Dev]

Good list of resources on XUL. I've had a lot of fun surfing the projects at mozdev.org. And had a few major browser crashes while trying them out. Best to make sure that the Mozilla profile is backed up first as something I tried once--been so long I don't remember which one--corrupted some of the profile files.