I'm under XP and have the same message as zenox. (noticed it also in 7.0.1 before upgrading to 8.0).
I will have the tests now to see if any change. Probably it will be more noticeable with FF 9.0 and the direct2D support.
Edit: Well I was able to play Trashoid Attack at an average of 14 FPS, but this time, compared to the last one I did, the attack propulse the ball more ahead which makes the game far more playable.
Also I tested my "Space Jinx" and it feels less laggy. Still going on with my tests, I'm pretty happy so far, it feels better/steadier.