Third-party cookies are cookies that are set by a website other than the one you are currently on. For years, brands have been using them to track website visitors, improve the user experience, and collect data that helps them target ads to the right audiences. They are also used to learn about what their visitors are checking out online when they aren't on their websites.

You can learn more about cookies here.

Because Chrome, Safari and Firefox will all no longer support this type of data tracking by 2022, publications like Digiday are calling Google's phase-out the "death of the third-party cookie."

Firefox call this cookie blocking technology "Enhanced Tracking Protection"  and is indicated by the shield icon to the left of the website address bar

Clicking on the shield will show current status for the current site

Mozilla (Firefox) have produced this article explaining in detail what the shield does and how to manage issues

Google Chrome have a setting which blocks third party cookies by default and is indicated by the 'third party cookie' icon to the right of the website address bar

Clicking on the icon will show the blocked cookies for the current site