Replace .AVIF image files with .JPG image files

Greetings... Unfortunately, I have encountered a problem associated with image files that appear on select websites. Instead of the customary .JPG format image files, .AVIF image files are being used. As a result, these .AVIF image files do not appear in Windows File Explorer nor are they usable in my specific purpose. In Firefox about:config, is there a way that I can disable the support of .AVIF image files so that only .JPG files appear and be downloaded? Also, is there some "easy" way to convert an existing .AVIF image file to a .JPG file without image degradation? Please advise. Thank you very much for your assistance! Take care...be well... ...ted benjeski