Facebook & I do not get on as I'm not happy giving them personal details to intentionally or otherwise share e.g. when they get hacked. Both accounts I have had are now suspended.
Relative to this thread the first time I opened an account I had the linked email online Yahoo account open at the same time. As soon as registered and active a list of people I might know appeared. Facebook could only have got these by either directly reading the email account address book or a cache, cookie etc on the PC. The second time I created an email account just for Facebook.
Since then generally I have been a lot more cautious by using private windows that clear cookies and page caches when closed, if websites will not work in private windows manually clearing cache and cookies, using cookie blockers in uBlock origin ( annoyances section ) and if needing email open at the same time as anything else having that in different browser.