Firefox Nightly Build was out on 1 April, and i tested its Metro version the next day and can say that its looking better than its predecessors, much more stable and Faster.
It still has a need of refining and streamlining, Most of the features of Nightly and Firefox are same and Firefox is just getting ready to receive its Metro counterpart for Work on Windows 8.


Most of the Desktop version features are not there in the Metro (Modern or whatever they call it ) version, like updating settings etc., it can be only used for browsing and making bookmarks etc.

To be Honest, I can say that the Nightly Build felt much more faster and approaching Chrome like HTML5 readiness, its HTML5 scores are significantly better than the v20 Firefox and which had only sub 400 scores out of 500, but Nightly breaches 400 barrier on both its Desktop and Metro Version.
Some screenshots from the Nightly are added :-