Cannot get dropped folder information in FIrefox 48

问题

I cannot get dropped folder information, in Firefox 48, Windows 10. event.dataTransfer.files.length is 0, when I drop folder. It works fine when I drop file.

If you know a recommended method to get dropped folder information, I wish to know it.

You can reproduce it in https://jsfiddle.net/0GiS0/4ZYq3/.

来源：https://stackoverflow.com/questions/38757322/cannot-get-dropped-folder-information-in-firefox-48