This does appear to be a case of there being an actual spec issue with the image, and Firefox being more strict than Chrome. If anyone is curious I can post the exact errors (although they're rather verbose), otherwise I ran it through the AOM validator[0].

I'm finding two relevant Firefox bug about being more strict than Chrome[1][2], but neither of them seemed to cover this case specifically. I'm considering filing a bug about it, but doing so would link my bugzilla account (full name and whatnot) with my HN account.

[0] https://gpac.github.io/ComplianceWarden-wasm/avif.html [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1689806 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=avif-compliance

Apparently newer versions of Chrome are equally strict and would also produce an error. The issue is now fixed.[0]

[0] https://github.com/lynnandtonic/nestflix.fun/issues/65