A new Firefox extension allows users to drag files into the attachment field instead of browsing for the file each time. Here is what the author has to say about the extension:
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.
It looks like this extension is pretty nice and it will make it a little more convenient for those people who handle attachments frequently. If you have to attach a lot of documents then this extension is extremely wonderful since you just have to drag all of the files over at one time instead of using GMail’s one file at a time attachment process.