Even though it may, for now, be a largely symbolic move, I’m quite proud of those responsible for this. Bravo!
When an internet user hits a web page that has been blocked for legal reasons (read: censorship), they may be presented with a 451 error instead of the more generic 403 “forbidden” error. This is a win for transparency.
Source: The HTTP 451 Error Code for Censorship Is Now an Internet Standard | Motherboard
The problem, of course, is that Facebook is not only blocking links to that domain, but also links to articles talking about it. You probably can’t even see this post on Facebook.
Source: Facebook is censoring links to competitor social network Tsu and deleting old mentions