I've looked into this before and haven't had much luck. I'm sure there are people out there that have wanted to do the same thing, so I'm resurrecting the question!

How can you limit the allowed extensions in a FileIframeField in ModelAdmin on the client side? I.e. set the extensions in the 'Files of type' combo in the file upload dialogue.

I've been able to do this on server side using a validator (i.e. an invalid file extension is discarded upon upload), but it would be much nicer if the files were automatically filtered in the dialogue before the upload. But how?