From Bug1482150#c1 - Allow multiple consumer to subscribe to device list notification callback in Gecko. I am moving that part on a separate bug because it requires some more thinking. Currently notifications are not possible for wasapi and OpenSL ES backends because the corresponding method is not implemented there. MediaManager::OnDeviceChange() callback is triggered from CamerasChild::RecvDeviceChange() even for audio changes. I need to verify if this is intentional or side effect.