A number of incidents ($#it) happened and suddenly every downloaded jpg picture would be jfif type! I have never even heard about any jfif format, so I was quite "surprised", to say the least. After some searching, I have a formula to repair such situation:
Start > Search > regedit > Computer\HKEY_CLASSES_ROOT\MIME\Database\Content Type\image/jpeg > rightclick Extension > edit > replace .jfif with .jpg > [Exit]
Start > Search > regedit > Computer\HKEY_CLASSES_ROOT\MIME\Database\Content Type\image/jpeg > rightclick Extension > edit > replace .jfif with .jpg > [Exit]