You can compile it by copying canvas3d/ to $my_firefox_source_dir/extensions/canvas3d and adding
ac_add_options --enable-extensions=default,canvas3dto your .mozconfig.
The tests are at the usual location. If you do actually get the extension built and running and the tests going, please drop me a note. I've only tested on 64-bit Linux using the proprietary Nvidia drivers, so feedback on the Windows-OS X-Linux 32-bit-ATI-Intel -axis would be most helpful.