Facebook complains that they are violating their terms of service by interfering with Facebook's user-interface and not using the official API. They also claim to own the "FB" set of letters and say F.B. Purity must remove those letters from it's domain and product. And finally, Facebook also complains that his website is spam and therefore direct links to it is blocked from Facebook.
The developer is not yet banned from Facebook, but has been told that his personal account will be banned at anytime, along with the Facebook page set up for F.B. Purity. This isn't the first time F.B. Purity has caught the eye of Facebook's legal team, but it is the first time they've decided to outright ban the developer. However, it's impossible to ban the browser extension because it is... well, an extension to your browser. Facebook probably can't even detect one is using it."