XULRunner is a free platform for running components for Firefox and Thunderbird, designed for XUL XPCOM application developers and, in fact, is an analogue of COM from Microsoft. XULRunner helps you get rid of a huge number of conditional compilation directives when creating Gecko applications. This environment has also been used to create several "stand-alone" programs: Songbird, Miro and MusicBee players, Instantbird IM client, Conkeror's full-fledged web browser, eMusic Remote digital music purchase tools and a number of other projects. Some programs use XULRunner technology to implement network access modules. Thanks to the libxul solution, which is part of the platform, independent developers can "integrate" some of Mozilla's technologies into their own products.
Initially, XULRunner was "ground" for the creation of various toolbars and other auxiliary components for Mozilla software. XULRunner itself does not have a graphical shell. The successful launch of the platform will be indicated by a window with a list of basic options and commands.