looking at observation 24986109 (https://www.inaturalist.org/observations/24986109), the sound file associated with it (https://static.inaturalist.org/sounds/38536.wav) is interesting because it is encoded at an unusually high 2822kbps bitrate, which translates to a 32-bit stereo wav file. (for comparison, CD quality sound would be equivalent to a 16-bit stereo wav file, or 1411kbps.)
when you look at Firefox’s console, you’ll see this warning message when trying to play this file from the observation page: Media resource https://static.inaturalist.org/sounds/38536.wav?1557653341 could not be decoded, error: Error Code: NS_ERROR_DOM_MEDIA_METADATA_ERR (0x806e0006).
i suspect this means that Firefox simply doesn’t know to decode very high bit depth .wav files.
i’m not aware of an easy way to identify audio files stored in iNat that are 32-bit wav files other than by downloading them to check their properties, but i would guess that any observations that have such audio files would have the same problem as observation 24986109, and if that’s true, then this seems more like a Firefox problem than an iNaturalist problem.
time to close this thread? (also time to close this related thread https://forum.inaturalist.org/t/sound-files-not-playing-in-the-inaturalist-player/6236 ?)