There's all sorts of current applications that won't work on ARM-based Windows 8 tablets when they emerge. Mozilla's looking to sidestep that restriction, with plans for both traditional desktop and Metro versions of its browser application. Mozilla's plans are outlined in its 2012 roadmap document, which you can read here.
It's certainly a fairly bullish document, given that it kicks things off like so
In 2012, Firefox will deliver incredible user and developer experiences in four areas.
The plan calls for a proof of concept version of Firefox for Metro by the second quarter of the year, although it's noted that this is very early stuff, and somewhat dependant upon Microsoft itself
This is not a Alpha or a Beta, but should demonstrate the feasibility of Firefox in Windows 8 Metro. (Timing here is dependent on when Microsoft releases their Windows 8 consumer preview and developer documentation.)
The alpha/beta stage should follow in the second half of the year, with the beta version intended to be 'feature complete'. Clearly, Mozilla feels that Windows 8 may be along sooner rather than later. [Mozilla via Ars Technica]