-Simon told me on IRC once Firefox removed support for Linux sound or something of that nature.
This is some grade A, honky *******.
Two common methods on Linux to have audio:
Hardware <- ALSA <- App
Hardware <- ALSA <- Pulseaudio <- App
ALSA works, but can be nasty to configure manually. Pulseaudio is allegedly simpler to program against, but, depending on hardware, might introduce lag or stutter. Many Linux distributions ship with Pulseaudio by default, and if it works, it's fine. It has some benefits too, like per-app volume control.
Firefox dropped the raw ALSA support, and works only with Pulseaudio. Now I have no sound in Firefox. I can adjust, I'll download videos or watch twitch streams in VLC. Nice side effect is that twitch can't serve me ads because I don't use their web player.
Lix calls Allegro 5, which then calls Pulseaudio or ALSA as available. I'm okay with the extra abstraction here because I want easy platform-independence.
It's always a tradeoff: Too little abstraction slows your app development. Too much abstraction brings more bugs in the layers. It's far simpler on Windows, where everybody can call DirectX and things will work.
-- Simon