Can you link to information about that vulnerability? To prevent a delay in your post appearing, add a space before the .com or .org in your link. (Otherwise, the reply is sent to the link spam moderation queue.)

Is it this one? https://besteffortteam.it/mozilla-firefox-content-type-confusion-unsafe-code-execution/

I think this is what they're doing:

https://www.jeffersonscher.com/res/test_jpg.php

Adding screenshot of download dialog:

That was the site I saw about this issue but no official notice or fix which is what is needed.

If you use my test document you will see that Firefox 96 still works the same way: when the server indicates this combination:

Content-Type: text/html Content-Disposition: attachment; filename=test.jpg

Firefox corrects the file name during the save process from test.jpg to test.jpg.html and you can open it as an HTML page rather than a corrupt JPEG image.

I don't know whether anyone has filed a bug. Normally security researchers would have done that before making a public disclosure but it is hard to search for security bugs.

If you want to file a new bug:

https://bugzilla.mozilla.org/