I may not be a huge Firefox 4 fan, but I do like it and I use it, along with Chrome, on my Linux and Windows boxes. On my Macs Minis, I tend to use Safari. My wife, on the other hand, loves Firefox and uses it on her latest MacBook Pro all the time. Until that is, she updated to Firefox 4 and discovered that all her Firefox multi-touch goodness was gone.
She was no longer able to pinch in or zoom out of her Web pages with a few gestures on the MacBook Pro's touchpad and she was not a happy camper. And, if she's not happy, I'm not happy.
After playing around with it for a while, I elected to fix it the brute-force way: I uninstalled Firefox 4 and brought back a copy of Firefox 3.6.16 from her Time Capsule using Time Machine. In passing let me say that Time Machine is the best backup and restore program out there on any operating system. You just set it up once and then you don't need to think about it every again until you still recover something and then recovering a file is as easy as one, two, three.
If I hadn't a backup, I would have downloaded an older copy of Firefox. While older versions don't seem to be available on the main Firefox site, you can still find them on such sites as Apple's own download site.
Although Mac users are the ones running into this problem, Windows and Linux users that have multi-touch capable touchpads have this problem as well-there just aren't that many of them compared to Mac multi-touch users. Hopefully, Firefox will activate all this functionality by default in the first update. After all, it harms no one to have multi-touch ready to go and they'll make the people, like my wife, who already use it constantly happy. It sounds like a win-win to me.