Note that this meme is a reference to that one Firefox user, and Firefox doesn't let the tab music thing happen, it auto-mutes background tabs (in a way where it doesn't do it when you want background audio to play)
Firefox has to my knowledge never done this. It absolutely doesn't do it currently. And like chrome it provides an icon on tabs playing sound so you can easily mute it with one click.
I think they meant that it doesn't start playing until you select the tab. If a video tries to start playing in a background tab, Firefox won't let it, but it won't stop videos that are already playing
