Facebook recently announced that they will begin offering a first-party cookie option for the Facebook Pixel. Previously, they only used third-party cookies. From their documentation:

You can now use both first and third-party cookies with your Facebook pixel. The difference between first and third-party cookies lies in who owns the cookie.

First-party cookies are owned by the website a person is currently viewing, while third-party cookies belong to a website other than the one a person is currently viewing. Compared to third-party cookies, first-party cookies are more widely accepted by browsers and stored for longer periods of time.

The option to use both first-party and third-party cookies will be released on October 24, 2018.

My questions are:

  • How does this work technically?
  • How can a third-party JavaScript script set a first-party cookie?
  • What was preventing Facebook from doing this before?
  • What are the implications for the user's privacy?
  • Does this successfully get around Safari's new intelligent tracking protections?

I'm searching for the technical details that haven't been included in Facebook's announcement.

  • 2
    1+2. Javascript loaded on the main page runs in the main page's context, no matter where it comes from. 3. Nothing, but it didn't behoove them because they got more from 3rd party cookies, until they didn't. 4. bad. 5. seemingly.
    – dandavis
    Oct 8, 2018 at 15:34
  • Extra question: how does Facebook track a user when it has no access to its own cookies?
    – Sam
    Oct 11, 2018 at 7:21


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