ChatZilla is normally used as part of SeaMonkey, or an extension to other browsers. However, this has caused problems with custom themes and other extensions, and means you can't restart the browser without leaving IRC.
XULRunner allows you to use ChatZilla standalone, free of whatever happens to your browser.
If you need to copy over settings or scripts, use the ChatZilla command /pref profilePath to find your profile.
On Windows and Linux, XULRunner checks regularly for new ChatZilla versions. Updates are not downloaded without your permission.
You can get more information on the update process, or subscribe to my news page to hear about new versions.
Since 0.9.71, the Extension manager can be opened from the ChatZilla menu.
I have one extension (Windows only): MinimizeToTray for ChatZilla.
0.9.83 is the latest available ChatZilla build. Development builds of ChatZilla will be posted here when vaguely significant changes are made.
You don't need to build Mozilla to build ChatZilla, but you do need bash, perl, and zip.