Firefox 4 is based on the Gecko 2.0 Web platform. This release features
JavaScript execution speeds up to six times faster than the previous
version, new capabilities for Web Developers and Add-on Developers such as
hardware accelerated graphics and HTML5 technologies, and a completely
revised user interface.
XULRunner is a runtime environment for applications using the
XML User Interface Language, XUL. It is the successor of the "Gecko"
runtime environment.