There appears to be a newer version (18.104.22.168) but I cannot download it from the Flash archive -- 404 error. It seems to have been pulled. Anyway, I'm currently using version 22.214.171.124, and it has been working great with the AOSP browser.
If you're going to use Firefox, try Firefox Beta. The beta version has always worked better for me. In my opinion, the AOSP browser works best with Flash, and the AOSP browser is still the best browser on Android. Although, with Chrome Beta, it's clear to me that Google is working hard to improve Chrome. However, you cannot beat fullscreen mode with quick controls, and if those are implemented into Chrome Beta, I won't use the AOSP browser nearly as much.
I use the AOSP browser about 80% of the time, and Chrome Beta about 20% of the time. I keep Firefox Beta installed when I want to browse via a SOCKS5 proxy.