As email shifts to webmail, we look for the same desktop convenience. The "dragdropupload" add-on for Firefox allows you to "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 Google Mail is possible to drop the files directly over the. 'Attach a file link."

Among other things, this makes it really easy to send a snapshot from your windows desktop (such as with snagit) to someone via webmail.

Get it here: https://addons.mozilla.org/en-US/firefox/addon/2190