On Windows, as part of our work to move GPU access and win32k system calls out of the content process, we are moving accelerated Canvas 2D to the GPU process.
I am nearly ready to enable this by default on Nightly and would really appreciate it if people running Nightly on Windows would do some initial testing to shake out any serious problems first.
In order to help, firstly update to the latest Nightly, to make sure you have some fixes that have just landed.
Then, to enable remote 2D canvas, in about:config set gfx.canvas.remote=true and restart Firefox.
Please file any problems you find as bugs blocking: