I've made the same experience: AVIF images sometimes look strange in Firefox (AVIF support behind a feature flag), but they look good in Chrome. I think Firefox might use the OS AVIF decoder, because the images also look strange when I open them directly on my Windows machine.

I can see the differences in Chrome too though? I came to the comments to see if anyone else could tell that the AVIF example is inferior to alternatives.

I was seeing the difference in chrome, but on linux.