Firefox Nightly no longer opens in Metro...

I was able to open Firefox Nightly in full screen Metro mode back when running the 90 day eval Enterprise version of Windows 8. But today I tried it again and it will only open in desktop mode. This is with ALL defaults assigned to it. I've been running the full Windows 8 upgrade the past two weeks.

I wonder what broke it?

Hey did you figure it out?
My ff nightly also only opens in desktop mode.
Edit:
Got mine to work. I had the wrong version installed.
You might want to try this one.
https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-elm/