engine - 11:56 am on Oct 5, 2012 (gmt 0)

For those of you running the RTM release of Windows 8, you can now download a nightly build of Mozilla Firefox from the Elm development branch and start testing. Elm is the experimental repository where most of our Metro development work has been happening. Firefox 'Metro' Preview For Windows 8 [blog.mozilla.org]

It's also interesting they are still using the term 'Metro'

Microsoft's 'Metro' Is No More, It's Windows 8 UI [webmasterworld.com]