Looks like any host which contains "facebook" gets blocked by this addon
That's true,the code which applies the built-in blocklist for well-known hosts isn't working correctly which is a known issue.
I experienced the same for fuckoffgoogle.de and nomoregoogle.com before I added them to the built-in whitelist.
I'll have to rewrite the blocklist logic to only care about full domains and not about domain parts.
Let's see if I'll be able to do that for the next release,there's much stuff to do in the issues.