dragdropupload by Emanuele Ruffaldi

“Drop files into attachment boxes instead of browse for them or type in the filename. Drop multiple files and fill all the entries. In some websites it allows to add new upload files: in Gmail is possible to drop the files directly over the “Attach a file” link.”

I’ve tested it with Netvibes’s Box.net module and Gmail and it works like a charm. Pretty useful and as others said that should be a standard behaviour in Firefox