With AMD GPUs the "direct mode" implementation is not quite ready, so when doing stuff with SteamVR it's a very good idea to disable compositing.

Except then with firefox 55 https://bugzilla.mozilla.org/show_bug.cgi?id=1377950 happens and you have to close all tabs and reopen them.

I don't want to bash mozilla for this bug. Bugs happen. But this has been known for over a month and firefox 55 released with it...