Metro Firefox is now available! Firefox has released its Windows 8 compatible browser in release preview mode! Firefox for Windows 8 looks truly awesome. To use new Metro Firefox you need to set it as your default browser. Else you will see the desktop regular version of Firefox. It is not the final version of Firefox for Windows 8. It is the Nightly build that meant for testing purpose. So you may experience some bugs.
As Firefox metro is for touch interface, you can experience metro touch and swipe gestures, Windows 8 Charms integration and beautiful interface called Australis.
Source : Firefox