Why do images on Amazon Books download as avif instead of jpeg?

This is a format designed for smaller file sizes and faster loading pages, but that concerns Amazon's servers. Firefox and any browser simply downloads the file provided by the server. You might need a conversion tool. So maybe Amazon updated their image system format.

I tried doing the download on Safari and it automatically shows up as a jpeg like it used to on Firefox. I prefer using Firefox but I don't want to add an extra step to me process which is what I have to do now. The platform I use for my email newsletters (Mailerlite) does not recognize the avif file type so I have to open that file using preview on my desktop and then export it as a jpeg back to my desktop. So, I kinda think it could have to do with how Firefox is handling the file being dragged to the desktop??