Not sure if this is several years too late, but I'm using the latest version of Mozilla Firefox (68.0.1 64-bit) and have reloaded the page several times to the same error box -
TypeError: WEBAudio.audioContext.listener.setVelocity is not a function.
I have given it several minutes between each reload (I figured it was my crap bandwidth) with no change.
Is there something I need to adjust in MF's setting?