Would be great if you could start to care about Firefox on Linux, too. (It's the only platform where hardware acceleration is disabled for example https://bugzilla.mozilla.org/show_bug.cgi?id=1280523)

Yeah, it's really weird that you STILL have to force enable it through about:config. Come on Mozilla… Mesa 17 has arguably the best OpenGL implementation ever.

I can confirm that the 57 beta has acceleration enabled by default on Linux.

Are you sure? You need to check about:support, as the checkbox in the settings does nothing on Linux. It still says

HW_COMPOSITING blocked by default: Acceleration blocked by platform

for me with Nightly (57) on Linux.