Not too far back, Facebook made what they called a change in their security procedure. It was a lie, as far as “security” goes.
When you logged on the first since the new procedure was inaugurated, they took you through some steps they claimed was to identify the use of the computer that you were using was truly YOU, and then from that computer they’d never have to ask again. Somehow this was supposed to BE SURE it was you logging into Facebook from that computer.
It was a lie.
What really happened after that?
After that, all you had to do was initiate ANY Internet connected activity and Facebook then knew you were ON the Internet.
That fact was made apparent by messages you started to get from Facebook - “notifications” - when the only thing you had done was open your browser, or start your POP Email client software and ask it to look for new Email.
What Facebook did was that recorded your PC as “you” and then scraped Internet traffic data, just like Google, to see (without you logging onto Facebook) anytime “you” popped up, in affect notifying Facebook you were “on”.
You can honestly imagine there is more; like the possibility that Facebook is also now monitoring ALL your Internet activity and building a “social identify” of who you are.