The Metro Firefox browser Nightly builds has been released for Surface Pro Windows 8 finally. The app designed specifically for touch devices, is for testing purposes only. If you have used Metro Firefox Preview on Windows 8 device, it will rolled out the update for Nightly testers.
Apart from the user interface improvements, there is also many changes under the hood performance improvement as well as some new features, such as use your mouse wheel to scroll up and down web page, new tile icon, a splash screen, choose from different tab styles, make special bookmarks, share Charms, and more.
Once installed Metro Firefox on your Surface Pro, you need to set it up as the default browser, so that you would run it in Metro interface from Start Screen.
* Download Firefox Metro for Windows 8 from mozilla.org (This is a direct download link)