Very poor flash performance

Hi. For some reason i have a very poor performance with flash 10 most noticeable when viewing flash video’s (on Youtube for example).
When I hover my mouse over a video the video drops down to like 1 FPS and overall it feels as if it isn’t using GPU acceleration even though I enabled 3D acceleration in the flashplayer options.
My Ati drivers are setup correctly (fgl_glxgears gives me 2400 FPS).
What could cause this and how do i fix it?
I use Firefox 3.0.10 99% of the time. For specs see my signature :).