there is a drag and drop firefox extention.
also, you cannot use a div, it has to be a file input tag.
but don't forget about CSS opacity and z-index (hint hint)
BROWSER STATS [% share]
(2013/10/31) IE7:0.5, IE8:8.6, IE9:5.3, IE10:12.3, FF:17.7, CH:41.8, SF:8.1, MOBILE:20.4