Earlier quoted context omitted.
Hardware acceleration is disabled by default because many graphics drivers suck and will break the browser if hardware acceleration is turned on. You can just go into the settings and turn it on (and then off, if you have problems). Chromium disables hardware acceleration by default for a wide swatch of graphics drivers too (including all Nvidia GPUs).
On my current Linux system with NVidia drivers, HW acceleration is enabled according to chrome://gpu (there are many accelerations and some are disabled, but many are enabled including Canvas and Compositing). Regardless of all, Chromium works just great, including smooth scrolling and WebGL, and Firefox doesn't (laggy scrolling, slower WebGL than in Chromium). I don't think the problem is with drivers but with Firef…
Chromium also has hw accel enabled by default for intel drivers, which is by far the most used gpu driver on linux (and is pretty stable in my experience). Firefox doesn't even have it enabled for intel