Firefox 59 no sound PulseAudio installed

I tried fvwm (on Ubuntu 18.04).

I got an error when launching Firefox 59 and later -- no sound.

https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues#w_you-may-need-to-install-the-required-pulseaudio-software

If you see a notification saying "To play audio, you may need to install the required PulseAudio software", it means that Firefox cannot find or use PulseAudio. Starting with Firefox 52, the PulseAudio software is required to play any audio from Firefox. Most Linux distributions now come with PulseAudio pre-installed.

https://support.mozilla.org/en-US/kb/no-sound-firefox-59-linux

If the PulseAudio service, which manages audio hardware, is not already running then Firefox will fail to start it due to sandboxing. Most desktop environments start PulseAudio when you log in and ensure that it remains running, and some newer distributions use systemd to manage restarting it, but if neither of these applies then this problem can occur.

Fix until FF 60:

pulseaudio --start --exit-idle-time=-1