[Extremely Extreme Extremist]

You don’t need a firewall. Just to go your “Tools” and then “Options” and you can block anything you want.

[library user]

If "youtube.com/xxxxxx" is anywhere in the source code of the website, I would think the content would be blocked as well.

Maybe disguise all the embedded youtube links by converting them via Tinyurl.

Just a thought. Not sure if it will work.