Yes, it's out of beta. If you're running Firefox 3-point-something, do Help → Check for updates and you should be offered it. Otherwise, visit firefox.com.
So far, so good, as far as I can tell with a few hours of light-duty surfing. But there is this one thing, which will be of interest to maybe no one? When composing a blog post, on Blogger, in Edit HTML mode, using the old-school editor, the keyboard shortcut Ctrl-Shift-A pops up the window to insert a URL. That keyboard shortcut still works, at least as far as Blogger is concerned. Unfortunately, that keyboard shortcut now ALSO means, to Firefox, "Oh! You want to open up the fancy new Add-ons Manager in a new tab! And bring that tab to the front, no matter what else you were doing! THIS IS ONE OF OUR MAJOR IMPROVEMENTS, WE THINK!"
Gahhh. I fail to see why having the Add-ons Manager in a new tab, instead of a separate window, is something to be excited about, but whatever. But I really fail to see why that item suddenly needs a new keyboard shortcut, when it didn't have one before, in every preceding version. I mean, it's not like Alt, t, a wasn't good enough, even for the mouse-hating extremists. How often do I need to Manage my add-ons, anyway? Not enough to need a new, other, keyboard shortcut which overloads one I was already using, that's how often.
Not for the first time have I wished Firefox supported remapping/reassigning/deassigning keyboard shortcuts. If anyone knows that this is actually possible to do, and can point me in the right direction, I'd be eternally grateful for months at least.
Dammit Zawinski, where are you when we need you?