Not sure there are any modern browsers that don’t support AVIF. Firefox, Edge, Chrome, Brave, Vivaldi, Safari, etc., all handle AVIF the same way. The only way to avoid this would be by using outdated browser versions.
Just a note, wget isn’t a browser—it’s a tool primarily used to download data.
It’s interesting to see how opinions differ on this. While you’re frustrated with AVIF support, there have been others who were upset when Edge didn’t support AVIF. For example, check out this discussion: https://stackoverflow.com/questions/75459594/why-doesnt-edge-support-avif-images
Regarding your other point:
You mentioned that the browser changes the image format when downloading. What I meant earlier is that you may need to edit or change settings yourself. If you save an image without editing, it will save in the format it’s currently in, which is AVIF. From your feedback, it seems you haven’t mentioned trying this or shown any screenshots. Expecting the browser to automatically convert to a different format than what the file is uploaded in isn’t typically how browsers operate.
About the example link you provided:
It seems similar to a discussion we had here: Image.jpeg is saved as .avif, unknown format - #5 by anon57438784. You might want to check out the extension mentioned there as a potential solution.