WebM(youtube) videos doesn't play smoothly about tenfourfox HOT 2 CLOSED

I'm closing this as invalid, not because the report itself is invalid, but 
because Firefox 4 on other software-only rendered platforms has similar 
problems due to retained layers, so this is a Mozilla problem and likely 
related to issue 7. As you would expect from a software rendering speed issue, 
performance is strictly CPU-speed dependent, and WebM videos do play fine on 
G5. I suggest voting for the Bugzilla bug in issue 7 as I don't think Mozilla 
is taking it seriously enough.

Opera lacks this problem because it uses a different graphics stack. By the 
same token, if Fx 3.6 had WebM support, it would probably also perform better 
than Fx 4 because it does not have retained layers.

I am investigating an accelerated path for WebM rendering using assembly code, 
but this will not occur for this release, and is unrelated to this actual 
problem.

I'm sorry I can't be more helpful, but I do appreciate the report.

As a followup, look at issue 28; I've spun off my comment above.