[anthony_franco]

Although it's not specifically in their terms, FB has a history[1] of trying to prevent unfriending apps (it's a cat and mouse game).

[1] http://socialfixer.com/blog/2013/10/27/facebook-doesnt-want-...

[deanclatworthy]

Yes, I'm aware of this. But the applications they went after adjusted Facebook (injected into the DOM), instead of leveraged their API to provide functionality through a Facebook canvas app, or externally.