So...
Hm... no input, huh?
I ran a test in downloading and uploading an image using Firefox and IE. No matter what was used to download the image in question, when it was uploaded, Firefox would should its MIME type as being image/jpeg and IE would show it to be image/pjpeg. I don't know if there might be some weird mechanics in JPEG handling in IE that would cause this, but I wouldn't write it off as a possibility. Either way, everything is theoretical at this point on my end.
I ran a test in downloading and uploading an image using Firefox and IE. No matter what was used to download the image in question, when it was uploaded, Firefox would should its MIME type as being image/jpeg and IE would show it to be image/pjpeg. I don't know if there might be some weird mechanics in JPEG handling in IE that would cause this, but I wouldn't write it off as a possibility. Either way, everything is theoretical at this point on my end.