[john70t]

A possible clue:
Whenever I played a .webm using Firefox, NoScript would block it a few times and then add it to the list of allowed permissions.

This of course leaves a history of .webm's played and creates a history of usage.
Manually deleting all of these permissions on file would be impossible.

CCleaner would normally not erase this history before, but apparently now it has started to. (I think.)

I set all permissions to "blocked" and rebooted Firefox with and without cleaning.
-Without cleaning, the permissions page stays blank after re-start. Nothing is shown. A blank page.
-With cleaning, all the websites are there again and enabled as "trusted"


EDIT: Definitely found the cause.
Erasing "compact databases" in CCLeaner/Applications/Firefox resets all the scripts, and then on restart Firefox defaults them to "trusted".
Just uncheck this box and your setting won't change.