With one of the recent Firefox releases (current version is 64), autoplay videos began to play again, although they start muted now [1]. None of the previously-working methods work (e.g. about:config media.autoplay.enabled), the documented preference is not there in 64 (promised for 63: either never happened, or was removed). Extensions that purport to disable autoplay do not work.
The solution that does work is set media.autoplay.default to 1.
Finding the working option required a bit of effort. I'm sure this post will become obsolete in a few months, and add to the Internet noise that makes it harder to find a working solution when Mozilla changes something again. But hey. Everyting is shit, so whatever.
[1] Savour the bitterness of realization that an employee of Mozilla thought that autoplay was okay to permit as long as it was muted.
December 18 2018, 22:12:31 UTC 2 months ago
So much for "diversity".
December 20 2018, 03:12:12 UTC 2 months ago Edited: December 20 2018, 03:13:33 UTC
Trying to figure out what these other options are supposed to do.