Firefox 4beta slower than 3.7a5?

ANyone here tried firefox 3.7a5 and/or 4beta? I’d be interested in finding out everyone’s experience because I found that when I ran the below web test, 3.7 got 60fps and 4b got about 22 fps!

Flying Images

You can find 4 here: Index of /pub/

And 3.7 here: Index of /pub/

Getting 60 FPS on Chromium 6 aswell.