We track most of our bugs in Bugzilla (https://bugzilla.mozilla.org). Once you've created an account, go to File a Bug, Core, and choose "Audio/Video: Playback" as the Component in the form.

(In general, it's fine to chuck bugs into Firefox -> Untriaged and they'll eventually land in the right place.)

If Bugzilla's a bit of a pain, just let me know and I'll happily file it for you.

Are Quantum bugs in bugzilla or Github?

Bugzilla. There are a few exceptions, but if you misfile a bug to Bugzilla, don't worry, it will be moved to Github during triage.

> Is there a location where I can submit a bug report?

You're probably looking for https://bugzilla.mozilla.org/enter_bug.cgi

There’s already one filed that you can track: https://bugzilla.mozilla.org/show_bug.cgi?id=1395158