When it considers them spammy, MFA & Co or finds them cloaking. (Didn't check the link ;))
601 karma · joined May 4, 2009
trolling 2.0?
If you wade through the thread, you'll see that someone posted that Firefox/Mozilla had it in trunk for nearly/over a year. Didn't check myself though.
I've reached it following links from the Alien Message submission on lesswrong.com
I've spotted another weakness though on the facebook login. The username's are generated as facebook_$firstname, which will lead to duplicates on big sites quite fast. I'd like to see a mechanism asking the users to chose a username.