I don't do fb, or know about these dark sites, but I thought some here may be interested. I think SifuPhil mentioned it once here in the past. http://www.wired.com/2014/10/facebook-tor-dark-site/
Tor, after all, doesn’t just let users hide their identities from the sites they visit, anonymously buying drugs on the Silk Road or uploading leaked documents to news sites through the leak platform SecureDrop. It’s also designed to circumvent censorship and surveillance that occurs much closer to the user’s own connection, such as in repressive regimes like Iran or China. And since Facebook uses SSL encryption, no surveillance system watching either Facebook’s connection or the user’s local traffic should be able to match up a user’s identity with their Facebook activity.