Rated 4 out of 5 stars

Very Good. Does just what its meant to do. Only downside is that if you block a site, you cannot use it for logging into other services. For example: because I blocked facebook, I cannot log into services using my fb account. I know this may be tricky to solve, but blocking a site w/o disabling the option to log through it could be an important feature.

This review is for a previous version of the add-on (0.6.6).