I'll click the button and when I go to paste, the box goes white and is unresponsive. I can't even X out of it. I have to reload the whole page.
I've tried it on a few themes and it's the same. Also, I don't know how to clear my cache (or even what that means).
Google Chrome. I ended up having to type the video tags by hand and it worked. Anyway, I'm really not very savvy when it comes to troubleshooting so any and all help is greatly appreciated.
It is indeed one of those strange occurrences, it might just need to clear on its own :/. When you went and deleted the browser history, did you select "Everything" instead of the default "from the past hour"?