In June, Firefoxmade its Total Cookie Protection (TCP) mechanism enabled by defaultfor everyone.
The feature had been in development for a long time and was introduced in a staggered manner.
His PrivacyTests.org website monitors the state of privacy protection across all mainstream browsers.

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Typically, cookies set by one website cant read the contents of cookies set by another website.
These are known as first-party cookies.
Clements explained that ad networks use this ability to set unique cookies for different websites.

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[TCP] certainly helps, but is by no means a complete solution for online privacy.
The TCP implementation makes an exception for certain genuine uses for third-party cookies to ensure websites work as expected.