XULRunner is essentially a runtime environment for XUL applications (Such as FireFox and ThunderBird). It will also allow Extension developers to create their extensions for use outside of the FireFox browser thereby (in the case of [http://chatzilla.rdmsoft.com/xulrunner/ ChatZilla]) allow the extension to keep running if the browser crashes.

* XULRunner as it is a separate application will allow extensions to run in their own process separate from FireFox. This will also keep the extension independent of any themes and other extensions. * Planned to be used by FireFox 3 when it is released Q1 2007. This will be version 1.9 and will be the first ''production'' version of XULRunner