In Webkit there is currently no way to determine if a file drop is a folder or not.
* Chrome returns a FileList with a length of 0.
* Firefox returns a FileList with a length of 1, but always reports a file size of 0 for folders, so you can provide a workaround.
* Webkit allows the folder to be dropped, and the file size varies depending on the folder contents.
Bump. This is pretty important to get fixed.