Describe the bug
I’m getting inconsistent results when converting AVIF images to other formats, using Firefox (in Ubuntu). I’m self-hosting Mazanoke 1.1.5, but the results are the same with mazanoke.com.

To Reproduce
Steps to reproduce the behavior:

1. Download this example AVIF file (as raw)
2. In Mazanoke, select Convert to: PNG
3. Drag and drop the AVIF file into the browser
4. Click the Download button of the converted file

Expected behavior
to receive a PNG file, fox.profile0.10bpc.yuv420.png

Screenshots
I receive a JPEG file, named fox.profile0.10bpc.yuv420.jpeg

Desktop (please complete the following information):

• OS: Ubuntu 24.04
• Browser Firefox 142.0.1

Additional context
The same thing (i.e. receiving a JPEG file) happens if I choose WebP as output, but not if I choose ICO: downloading the latter does produce a fox.profile0.10bpc.yuv420.ico, as expected.

Choosing JPG output also works as expected (although it would be pretty funny if it didn’t). Notably, this produces the filename fox.profile0.10bpc.yuv420.jpg: the file extension differs from the one produced by Firefox for the unexpected cases (.jpeg).

I can also work around the issue by selecting ”Download all”, which produces a zip archive, and all the files therein are in my chosen output formats as listed.

In Vivaldi (which is based on Chrome) the Download link also does produce the file in the chosen output format. So this looks like Firefox-specific issue.

Converting from (and to) other formats seems to work as expected in Firefox (at least the ones I’ve tested so far).