Mozilla is rolling out Total Cookie Protection by default to all Firefox desktop users. Per the company, this makes Firefox the most secure and private web browser, as cookies can now be confined to the site where they were created.
Total Cookie Protection is a feature that's destined to protect you against tracking without impacting your browsing experience. Basically, it will create a "jar" for each website you visit, which will allow websites to only see your behavior on individual sites. Take this example from the Mozilla Firefox team:
Any time a website, or third-party content embedded in a website, deposits a cookie in your browser, that cookie is confined to the cookie jar assigned to only that website. No other websites can reach into the cookie jars that don’t belong to them and find out what the other websites’ cookies know about you — giving you freedom from invasive ads.
Mozilla believes that Total Cookie Protection can help you enjoy better privacy and have a great browsing experience. It builds on existing tools in Firefox and is better than the browser's anti-tracking features. This is also harder to abuse, as with Firefox's Enhanced Tracking Protection, trackers were maintained based on a list, which let attackers set up new domains as a workaround. Total Cookie Protection solves that by restricting functionality for all cookies, and not just those on a list.