On two of my systems this test result went from about 6 FPS with Firefox 4 and 5 to about 33 FPS in Firefox 6 beta.
My desktop system has an AMD/ATI R710 GPU, and I use the open source r600g Gallium3D drivers.
My netbook system (Acer Aspire One 522) has an AMD/ATI C50 APU, and I use the open source r600g Gallium3D drivers.
These are both very modest systems in terms of GPU performance. On neither system does WebGL work with Firefox 6. Only hardware acceleration, to some extent.
I expect this to improve again in Firefox 7, but it is still true to say that it has already improved considerably in Firefox 6.