There are a variety of resources for people wanting to get started building XUL applications and extensionsÉ first of all there is a fairly comprehensive XUL reference at XULPlanet.com É you can find developer newsgroups at news.mozilla.org, and developer discussion in the #developers channel on irc.mozilla.org.

Mozilla.org is building out its own developer site which will eventually live at developer.mozilla.org, but which currently resides at developer-test.mozilla.org. If youÕre interested in contributing your time helping write documentation and articles, you should go here and pitch in. The goal is to be a developer community portal with reference documentation about the Mozilla platform, articles to help people get started and learn more, and provide links to off-site resources.

At the bookstore, you can get your feet wet in the realm of hacking Firefox with Firefox Hacks, part of OÕReillyÕs Hacks series of titles which provides an introduction to hacking the browser (useful for Extension developers) and Rapid Application Development with Mozilla by Nigel MacFarlane, a comprehensive guide to building applications with XUL.