Firefox 9 is out now (the public page hasn't been updated yet as of this writing, but the build is available from official links already), and while that in itself isn't really big news (the uberpopular browser updates all the time, and plenty of people have already chosen to use Chrome or another browser anyway), there is one big note in this update worth mentioning: The app will now natively support two-finger swiping gestures on your MacBook (or Magic Mouse or trackpad, if you have one of those running). That means that without extra add-ons, you can now swipe two fingers forward or back to browse through your history, in addition to the other usual gestures available to most apps, like using two fingers to scroll and so on.
The update to version 9 also adds improved theme navigation for OS X Lion as well, so that's a nice bonus. One thing that's not in the app yet is an actual Lion-style full-screen mode. Firefox has its own fullscreen mode, but it's not exactly the one-app view that Apple expects. And while Firefox is easy enough to install and update on its own, there's no Mac App Store version yet. Mozilla may not be interested in running updates through Apple's App Store, but it might be easier for users to do so.
At any rate, if you're running Firefox on your Mac, you should grab the update now. I personally like Firefox, but for some reason it's never run well on my MacBook, and I switched over to Chrome full time a few months ago. But it's a solid browser (aside from some issues with memory leaks, mostly having to do with Flash, in my experience), and this update adds a little more Mac-specific functionality as well.