If webgl.disabled is true set this to false. If that doesn't help you could try forcing it to be enabled.
Also, do you have the most up to date graphics drivers? This could be another thing to consider.
I should have mentioned I'm using the nouveau driver. I get slightly better performance with the proprietary nvidia driver. In my experience most games will either work about as well with nouveau or not at all.
Nouveau looks like a cool project, it's probably worth raising it with them as WebGL is going to be important in the future.
GT218 [NVS 3100M] xorg-x11-drv-nouveau-0.0.16-27.20110720gitb806e3f.fc16.x86_64