Facebook' Social Plugins
My interest in Facebooks's Social Plugins started when I saw it being used on a website (ThisInterestsMe.com) that I found when I was researching something. Actually, I can't remember what I was looking for. I think it was someting innocuous as the meaning of historical terms for my local history pages.
ThisInterestsMe.com uses the Facebook Social Plugin to data-mine visitors information.
Data Mining
As this is not understood it is the reason that a lot of people get into problems with data loss and potential hacking.

externalhit_ua.php
The primary purpose of FacebookExternalHit is to crawl the content of an app or website that was shared on one of Meta’s family of apps, such as Facebook, Instagram, or Messenger. The link might have been shared by copying and pasting or by using the Facebook social plugin. This crawler gathers, caches, and displays information about the app or website such as its title, description, and thumbnail image.