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But that site would have to know what your Facebook profile is. And with FB domains blocked outside of the FB container, they're going to have a harder time putting that info together.

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But that site would have to know what your Facebook profile is. And with FB domains blocked outside of the FB container, they're going to have a harder time putting that info together.

Nope. I didn't find a lot of activity here (most was wrong), but Albertsons and Home Depot had hits. I've never given either my Facebook info.

https://facebook.com/off_facebook_activity/

Could they just use your email address?

psst ... check out https://monitor.firefox.com/protect-my-email

That helps only for breaches involving specific email addresses. What the GP is hinting at is Facebook having your email address and you using the same email address on a site for a purchase. Sellers usually upload their customers' email addresses on to Facebook and other social media platforms so that they can target these users better. So if you use the same email address everywhere, then linking all your interactions and transactions is a certainty.

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