Firefox 57.0.2 is unable to play sound after switching to this Windows release. Also affects Nightly and Developers edition eg youtube video plays on chrome/edge not on firefox.
Logged and confirmed as a known issue by Microsoft.
Microsoft response Windows has several audio volume APIs - IAudioEndpointVolume, IChannelAudioVolume, ISimpleAudioVolume, and IAudioEndpointVolume. These APIs can be used to change the volume and/or mute state of the stream, app, or audio device.
In build 17063 a change was made to these APIs to have them return S_FALSE (1) if the requested change was a no-op.
This broke apps (like Firefox) which request changes (that may be no-ops) and then explicitly check the return value against S_OK (0).