Why does Firefox not show multiple output devices for Google Hangout audio (phone calls), while Chrome does?

by user3.1415927   Last Updated July 11, 2018 19:01 PM

I'm using soundflower to route audio to multiple devices on OS X 10.11.6. Previously (over a year prior), I was able to route audio to a 'Multi-Output Device' as set up in "Audio MIDI Setup." This MOD is still visible in that setup page, but Firefox does not show it as an option...

Only one option

There are still multiple devices available as input options...

enter image description here

... and the MOD shows up in Chrome. (...)

enter image description here

Why is this Multi-Output Device (MOD) not showing in Firefox? How can I get it to show up as an output option in Google Hangouts when used on Firefox? Using Chrome is a temporary solution, but I don't expect it to be long-term...

I have already tried creating a new MOD (as you can see in the Chrome screenshot).

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