When composing a message in Gmail, I noticed I can no longer drag and drop images into the message as I have done before. I then realized it's not just Gmail. I cannot drop any file into Firefox at all. Generally dropping a file into Firefox would open that file in the browser (assuming it's a filetype Firefox can open), but no matter what kind of file I try to drop, all I get is the "no symbol" icon (circle with a line through it), and I'm unable to drop the file anywhere on the browser. I've also started Firefox in Safe Mode and it still didn't let me drop anything, so it's not an addon/extension causing the problem. FYI, I recently installed Windows 10 x64 and have had a headache trying to solve UAC/Administrator/Permission issues so I'm wondering if that has anything to do with it. Running Firefox in Administrator mode doesn't fix the problem, however. I just updated to the latest version of Firefox as well. Issue still not fixed.