The last release/mention I found was a preview [1] in October last year and then nothing but tumbleweed ...
[1] https://blog.mozilla.org/futurereleases/2012/10/04/firefox-m...
I can guarantee you that people are working on it. I don't know the specifics, but it's coming along. You can follow the commits here [1]. Of course because it is free software, if you are not afraid to test a early prototype, you can get a build for every push to the repo. It is a bit complicated (lots of clicks in our custom CI interface), tell me if you are interested.
[1]: http://hg.mozilla.org/projects/elm/, the elm branch being the repo where people work on Win8 support.
- Find a green "B" on a Win opt line (meaning that a build has succeeded for a Windows Optimized build), click on it, a panel appears at the bottom
- On the bottom left of the page, you can see a link named "go to build directory". Click on it, that sends you to the location where the CI stores the build
- In the list, there is an installer executable, that you can use to install this particular Firefox build (for examples: "firefox-20.0a1.en-US.win32.installer.exe").
Please keep in mind this is very much a work in progress, and it is likely to break horribly, maybe destroying your computer in the process (you never know :D). No warranties, blah blah blah. If you find bugs, it would be much appreciated to have them filed on bugzila.mozilla.org.
http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/lates...
We hope to enable Metro in the main (mozilla-central) nightly builds within the next few weeks.