Great feature, I don't have twitter or facebook and I have to add separate extensions to block those annoying tracking features from every other sites.

To me any website that rely on facebook or twitter to log in is broken and I just don't use them.

I recently had one that required sending my info to xiti to display a js popup to log in with email. Too bad they lost a potential client for their service because their web page sucks and is designed with them in mind instead of the actual user.