This change will already do that; Firefox doesn't whitelist sites by default.
My personal preference would have been to mute tabs by default rather than blocking autoplay:
- Sites can't detect a muted tab with JS, so they can't use it for tracking or block services behind it.
- Nothing would break. Firefox did a pretty good job of minimizing the potential breakage from this change, but there are still edge cases and some weird logic that's required to address them. A muted tab is no different than you unplugging the speakers from your computer. It'll never cause a Javascript error.
- It's simpler from a user perspective. You can already mute a tab. Why do we need another control that's meant to fulfill the same purpose?
The counter-argument is that blocking autoplay is actually about saving data, but in reality:
- The restrictions are trivial to bypass, since you can just start playing after the first user gesture/action.
- Muted videos are still allowed to autoplay.
So if you're trying to save data, it would still be a lot better to just have an option to block audio/video entirely, not just of the autoplaying variety.
As far as I can tell, Mozilla basically got kind of railroaded into this implementation because that's what Google did, and that set the general narrative. Mozilla ended up with a better implementation than Google, but this is still one of those restrictions where I feel like 2-3 years from now we're going to look back and say, "yeah, this wasn't really thought through all the way."