I told you a little earlier that one of our major goals this year is developing XULRunner further and provide a vehicle for allowing people to make XUL applications really easily.

XULRunner applications are packaged in a similar fashion to Firefox extensions. There are chrome sections (XUL, JavaScript, skins, etc), XPCOM components and defaults, but the housekeeping is slightly different.

An Application Manifest provides the XULRunner with information about the application, and provides the system shell with things like icons for display.

The concept is somewhat similar to MacOS X application bundles.