I was gonna make a similar thread myself, glad I noticed this one.

How to properly tell autoplay to fuck off:
media.autoplay.allow-extension-background-pages = false
media.autoplay.block-event.enabled = true
media.autoplay.block-webaudio = true
media.autoplay.default = 5
media.autoplay.blocking_policy = 2

You can reenable permissions on a site by site basis from the button next to the url bar. The change can take a bit of getting used to (you sometimes have to click play multiple times on some websites), but it saved me countless annoyances especially on those god awful YouTube channel pages that just won't shut up no matter what else you try.