Sound problems on Ubuntu 18.04 LTS

[マスターズ・イアン]

OK, an update ...

While looking at this page:
https://help.ubuntu.com/community/SoundTroubleshooting

I did:

$ aplay /usr/share/sounds/alsa/Front_Center.wav

output was:
Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono

which produced no sound, but:

$ sudo aplay /usr/share/sounds/alsa/Front_Center.wav

did work and I heard the sound file.

According to that page, running the following command:
sudo addgroup <username> audio

  should have fixed it, but it doesn't.

So I logged in as root (I know, *really* not a great idea) and have the following environment.
1. Settings > Sound is completely empty but
2. Sound plays in Rhythmbox
3. No sound in Firefox

More later, I expect.

Ian