Some websites embed Facebook plugins, e.g., comment with Facebook, Facebook messenger live chat, etc.

The first time I visit one of those sites, they already know my currently logged in Facebook account.

How is that possible technically?


Because Facebook knows your browser. When you logged in, it almost certainly set cookies, but it can identify your browser in other ways, like your IP address, installed add-ins, et cetera and so on.

Since the plugins are also served from Facebook's domain(s), it can "see" your browser when you visit other sites, so it knows it's you.

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  • Other websites cant access fb cookie or localstorage, right? I can make comments/likes in those websites. So they can do that too, without my consent? – Akivamu Jun 21 '18 at 18:07
  • You consent when you log into Facebook. I'm sure it's all there in their Privacy Policy. Other sites can't access the data, but Facebook can give it to them. – ale Jun 21 '18 at 18:41

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