3 (sic, three) FPS here-- Linux Mint 12 amd64, Firefox 9.0.1, nvidia Go 7300 with 512MB RAM and 4GB system RAM. Also only about 60% of the frame is visible at a time on my 1280x800 display.
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