Firefox does support ultrasounds

[somini]

The bug you mention in the Readme was fixed on Firefox 44. https://bugzilla.mozilla.org/show_bug.cgi?id=953265

I tested ultrasound transmission from Firefox Android to Firefox Desktop and it worked with minor packet loss.

[somini]

I tested the other way around(Receiver on Mobile, Transmitter on Desktop) and it also works.

[dcelasun]

Indeed, it worked with Firefox 61 on both desktop and Android.

[makew0rld]

I can confirm as well, with Firefox Beta on Android, and Firefox desktop (Linux), sending and recieving with either device.