URL: https://www.youtube.com/
Browser / Version: Firefox, IE, and Edge
Operating System: Mac OS X 10.10
Problem type: Something else - I'll add details below

Steps to Reproduce

1. Navigate to: https://www.youtube.com/
2. Log into a YouTube account.
3. Copy some text and try to paste it into the comment field below a video.

Expected Behavior:
The clipboard text should be pasted into the comment field.

Actual Behavior:
In Chrome and Safari, the clipboard text is pasted as expected. In Firefox, IE, and Edge, nothing is pasted.