I have found FF to be a useless for audio playback - endless problems on several sites. I have found Brave to be splendid in all regards, including much faster page loading and no problems with playback (on Ubuntu Studio 19.04). Give it try! {It’s a fork of Chromium.}
I tried a few of the above examples, and the only one that doesn’t work is the .mpga file. But that may be an issue with the file type not being web-compatible or iNat-compatible?
FWIW, we just rely on the browser to play sounds, so results will vary based on browser capabilities. Some things we could do to address this include
Prevent people from uploading sound formats we know won’t play in most browsers (we already do this for some formats, but clearly we’re missing others)
Try to convert all sounds to a relatively universal format like WAV or MP3 (harder for us since we don’t always know if conversion will succeed).
Same results as initially reported, and they do all play locally if I download them from iNat. Given the responses above it seems to be working as intended and this is more of a web browser issue. Feel free to open up a topic in #feature-requests if you’d like to advocate for the options listed by kueda above. Thanks!