I recently ditched Firefox.
Firefox 52 on Linux broke audio by dropping support for the standard Linux sound subsystem, ALSA.
Instead, Firefox now requires PulseAudio. Pulse was originally intended to be a replacement for ALSA, but development stalled, and now it's just a routing layer that requires an actual sound infrastructure underneath it, usually ALSA.
Some people have got this "architecture" working perfectly adequately. Others complain of latency and glitches, or simply no sound. I don't see the point in even trying, since the existing structure works perfectly well.
It's the latest stupid decision by Firefox developers, and it was enough. I migrated to the Chromium-based Vivaldi browser.