thanks for reporting the issue @jsweeps. the audio files present in distill are in ogg format. firefox is refusing to play those files in the extension’s context. mp3 files work well. the workaround right now is to add your own audio files under the extension’s settings.
some good mp3 audio files can be downloaded from the following links:
https://pixabay.com/sound-effects/search/ping/
https://pixabay.com/sound-effects/search/bell/
i will check firefox’s bugzilla to see if this is a known issue.