According to the announcement:
The feature goal here is a new Gecko based browser built for and integrated with the Metro environment. Firefox on Metro, like all other Metro apps will be full screen, focused on touch interactions, and connected to the rest of the Metro environment through Windows 8 contracts.
The MozillaWiki has yet another page that goes into further detail on the organization's plans for Firefox to run on Windows 8's Metro UI. Mozilla will also release a version of Firefox that will run on Windows 8's "Classic" UI, stating:
Classic is very similar to the Windows 7 environment at this time, it requires a simple evolution of the current Firefox Windows product. Metro is an entirely new environment and requires a new Firefox front end and system integration points.
Mozilla working on Metro edition of Firefox
Posted on Monday, February 13 2012 @ 20:31 CET by Thomas De Maesschalck