Great Rated 4 out of 5 stars
Good but it'd be nice to recover the list of blacklisted sites if you make a mistake or change your mind. Maybe you could enter a password to recover them?
Also, if you follow a bunch of links on an site you shouldn't be on, you may end up filling your history with similar sites and you'd have to block each one. Maybe you could have an option that blocks all history except for sites you approve. Sort of like a reverse version?