This page is intended to answer frequently asked questions and correct common misconceptions about XULRunner.

Is XULRunner a browser?
No. You can use XULRunner to make a browser (mybrowser example or Firefox), but there is no such thing as "the XULRunner browser".
Is XULRunner a development tool?
Not particularly; XULRunner is a Internet technology runtime. XULRunner can be used to make development tools (the AJAX Toolkit Framework, for example). In the future there will be a XULRunner Developer Kit which will contain various development tools.
How does XULRunner compare to other runtimes like Java or .NET (or Python or ...)?
The goal of XULRunner is to facilitate development and deployment of Internet applications. It is not meant to be a full-featured runtime; this allows XULRunner to maintain a smaller footprint and simpler deployment strategy than generic full-featured runtimes.
If I use XULRunner do I have to write my application in XUL?
No! You can write your application in any language supported by the Mozilla web platform, including HTML, XHTML, SVG, or XUL.
So why is it called XULRunner, instead of HTMLRunner or something?
XUL was always the original language of choice for UI in mozilla applications and the main library is called libXUL, mostly the name is a hangover from that that has now stuck.
When will Firefox be based on XULRunner?
There is no intention to do this for official release versions of Firefox. It is already possible to run Firefox on XULRunner now though and certain Linux distributions already do this.
Why is installing XULRunner so painful? Why isn't there a nice installer?
Because nobody has written that code yet! This is a developer preview release: additional features for installing and deploying XULRunner and applications based on XULRunner will be available in future releases.
I'm writing a XUL application, how can I deploy that application to my users?
Right now Mozilla recommends that XULRunner should be deployed privately with each application. See Deploying XULRunner 1.8 for more information.
Where is the source code?
I think I've found a bug, how do I report it?
bugzilla.mozilla.org is used to track bugs in all Mozilla products. Please search to make sure that your bug has not already been reported.
How can I help?
If you want to help with XULRunner but don't know where to start, visit the XULRunner:Community page and ask questions on the newsgroups or the IRC channel.