Implementation of Facebook SDK Connect from 2014.
https://developers.facebook.com/
JavaScript Libraries and Functions · JavaScript Library
Get access to data on 91,291 websites that are Facebook SDK 2014 Customers. We know of 71,840 live websites using Facebook SDK 2014 and an additional 19,451 sites that used Facebook SDK 2014 historically and 33,505 websites in the United States.
Get a list of 91,291 websites using Facebook SDK 2014 which includes location information, hosting data, contact details, 89,663 currently live websites which includes 17,823 domains that redirect to sites in the list. 19,451 sites that used this technology previously and 33,505 websites in the United States currently using Facebook SDK 2014.