When don't we just use jack without pulse audio, most programs support it (VLC,MPV).
Firefox doesn't. They dropped all other audio systems except for pulse! Highly annoying.
This is just my own experience, but sound works fine for me with just Alsa (no pulseaudio or apulse). Although even the Arch Wiki [1] says differently.
[1]: https://wiki.archlinux.org/index.php/Firefox#Multimedia_play...
My main gripe with anything from that group of people is that they refuse to play nice with others, and by extension that their code refuses to work properly with code produced by others.