gecko-dev/xulrunner

XULRunner is a package which can be used to run applications written in HTML
or XUL. It can also be used to embed the gecko rendering engine into
binary applications.

XULRunner is not a product; it is a tool which can be used to create products.
It is a byproduct of Firefox development and the Mozilla community does not
have a strong commitment to support XULRunner development apart from Firefox
development.

For more information about using XULRunner or how to use this binary package,
see the Mozilla Developer Center article:

https://developer.mozilla.org/en/XULRunner