Firefox Nightly does, and it's not done by default in non-nightly (but you can enable it with "media.block-autoplay-until-in-foreground"). I imagine it will bec

Firefox Nightly does, and it's not done by default in non-nightly (but you can enable it with "media.block-autoplay-until-in-foreground"). I imagine it will become the default eventually. "Firefox doesn't do this" is not a valid one-sentence summary of what I just said.