It is working perfectly again with windows 10 (And I love it) But Not working at all in windows 8.1. It doesn't play any sound, not even the predefined one, and keeps showing the same error message...
There is a lengthy discussion about the Windows 8.1 playback issue over in the discourse support thread: https://discourse.mozilla.org/t/support-notification-sound/23758/18?u=freaktechnik
Installing VLC and using a FLAC as custom sound seems to have solved the issue. Really weird issue with the Firefox media decoder, this.
