[LAU] It's 2018 and ...

[Ralf Mardorf]

The official Arch Linux package was build with alsa and jack support
enabled.

"[snip]
pkgname=firefox
pkgver=59.0.2
[snip]
ac_add_options --enable-alsa
ac_add_options --enable-jack
[snip]" -
https://git.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/firefox

With or without alsa and jack support enabled
https://aur.archlinux.org/packages/apulse works well.


So for your distro it might be better to build apulse, which at a max
takes a few minutes, while building Firefox could take hours and tmpfs
might be to small to build Firefox in a tmpfs directory.