Meh, I typically use Chrome through a virtual machine with Spice which has broken OpenGL support, so I wasn't getting hardware acceleration anyway. I still get screen tearing in Firefox, for Christ's sake.
There is an easy fix for this:
Set layers.acceleration.force-enabled: true in about:config.
I believe this is because Firefox assumes it's the responsibility of the compositor you are running to properly vsync, but if you're not running a compositor you can turn on this option.
