As far as I know, there were some problems with an add-on so they're waiting until things are fixed. However, I could be completely wrong about that. You can get it here (although this will put you on the beta track, which will soon be 10): http://www.mozilla.org/en-US/firefox/beta/
From what I saw this is because a good portion of the Mozilla staff is away for the holiday so they're actually doing the official release in the first week or so of January once they're up to staff. They don't want to do any kind of major release and run into issues when they're down in numbers.