28/08/2019: Firefox 69 now fully depends on dbus
The upcoming Firefox release now depends on dbus and this dependency can't be disabled. The usual --disable-dbus option has no effect.
Until this is fixed upstream or we find a way to patch this out KISS will be swapping to the next ESR release of Firefox (68.0.2 -> 68.1.0). This gives us a little over a year to sort out this situation.
With the release of Firefox 70 ALSA support will also be dropped from Firefox and we will have to ship apulse with KISS to fix this.*
It seems to be getting harder and harder to run and maintain a system which doesn't follow the usual trend of software choices. Firefox even has a dbus dependency on FreeBSD and OpenBSD!
The upstream bug report can be found here: #1561207
*: Update: On inspection of the Firefox 71 beta, ALSA is still supported!
Update (Nov 3 2019)
I have written a patch to remove the dbus requirement in versions 69.0 to 71.0 beta. Firefox in KISS works 100% fine withoutdbus!
Why did --disable-dbus break?
Firefox 69.0 added a new audio feature called "audio_thread_priority" to prioritize audio threads. On Linux, this uses dbus to function.
Firefox has historically always provided the --disable-dbus option to remove the requirement. It has always been optional. The feature works in its entirety minus the new audio_thread_priority code.
No (or little) testing was done with the --disable-dbus configure flag and this is marked as a defect in the upstream bug report (which gives me hope that it'll be fixed).
My patch to workaround this issue simply disables the audio_thread_priority feature which removes the dbus requirement and effectively reverts audio to how it was prior to version 69.0.
The upstream bug report can be found here: #1561207