Even though I have mentioned it before, it’s worth repeating:
Another great addition for XULRunner developers – Microsoft symbol and source server support. Look here for information on Mozilla’s symbol and source server support. Just use
http://symbols.mozilla.org/xulrunnerinstead of the Firefox URL. This is a huge deal for helping developers debug problems using the non-debug releases of XULRunner runtimes and SDKs.
If you haven’t tried using XULRunner yet, now is a great time to start. Use markup/JS/CSS to build real desktop applications using native OS look-n-feel, with complete access to custom and OS binary functionality.