- Individual products like AdRoll and Perfect Audience let you track users and show them ads. Ever been to a site and had their ads pop up everywhere afterwards? Ever looked at a product then gotten ads for _just that product_? Yeah, that.
- Google lets you track conversions based on a ton of information. What Google ads users viewed, sure, but also referring site, region, demographic info. Hell, it'll tell you which pages you visited before buying. Everything but the search term you used ... unless the referrer was AdWords.
- Emails all send you unique links, which allow you to do conversion tracking. Hell, you can even embed retargeting pixels in emails, so when you open a company's email, they can serve you ads based on that knowledge.
Every possible way that tech can track you, companies are tracking and advertising with. I get that it's kind of scary, but it's not just Facebook, and a lot of it is the digital equivalent of reading body language on people in your store.
So, yeah, run an ad blocker. But not just for Facebook.