When dragging and dropping files onto assistant, one has to let the file go right over the upload area. Dropping the file on the background of the page just navigates the browser to the local file (at least on Firefox). It would be much better if the entire window of the assistant is "hot" for dropping files; this would make it a bit easier to drop no matter where your explorer window is.
Make the background of the Assistant able to accept drag and drop files.
