Time marches on and things change; in the tech world, even more so. The recent release of Firefox 52 for Linux rather quietly dropped ALSA sound in favor of Pulse Audio, which is now a "hard dependency". Oddly, this was not in the release notes - which seems like exactly the sort of thing that release notes are for.
Mozilla seems to be a bit sniffy about the subject, too:
Responding to the criticism Mozilla engineer, Anthony Jones, says: “making trade offs is a necessary part of making a good product”. When asked to restore ALSA support in the the rep replies: “[that] isn’t going to happen. Sorry.”
‘Installing Pulse Audio fixes all the known issues with the ALSA backend’, he explains, and cites telemetry usage as having informed their decision.Omgubuntu