XULRunner

XULRunner is a run-time engine for XUL. It replaced the Gecko Runtime Environment, a stalled project with a similar purpose.

The first stable developer preview of XULRunner was released in February 2006, based on the Mozilla 1.8 code base. It is developed by the Mozilla Foundation to provide a common back-end for XUL-based applications.

XULRunner is a "technology experiment", not a shipped product, meaning there are no "official" XULRunner releases, only stable builds based on the same code as a corresponding Firefox release.

Mozilla stopped supporting the development of XULrunner in July 2015.

XULRunner is a runtime that can be used to bootstrap multiple XUL + XPCOM applications that are as rich as Firefox and Thunderbird.

XULRunner stores a variety of configuration data (bookmarks, cookies, contacts etc.) in internally managed SQLite databases, and even offer an add-on to manage SQLite databases.

All XUL-based applications like Mozilla Firefox, Mozilla Thunderbird, Nightingale, Songbird, Flickr Uploadr, SeaMonkey, Conkeror, Sunbird, Miro, Joost, and TomTom Home 2.0 run on XULRunner. Starting with version 3.0, Mozilla Firefox uses a "private" XULRunner, meaning the framework is installed locally in the application directory.

The fourth version of the video game series Simon the Sorcerer, Simon the Sorcerer 4: Chaos Happens, uses XULRunner.

The eMusic website has a download application called eMusic Remote that uses XULRunner.