Almost in stride with its recent release of Firefox 19, Mozilla has announced the intention to block third-party cookies by default starting in Firefox 22.

Cookies are something that are stored on your computer by pretty much every website you visit. The purpose of cookies is to store varying amounts of information about you, such as your login details so you don’t have to always login when you visit your favorite website. Third-party cookies are cookies placed by websites which you haven’t directly visited. Third-party cookies are typically used by advertising networks (e.g. you visit a website that has ads and the ad network running on that website places a third-party cookie on your computer) to help serve better targeted ads, but they can be used for other purposes).

As ArsTechnica points out, Safari is the only other major browser to block third-party cookies by default. Internet Explorer blocks some while Chrome and Opera block none, although you have the option to manually modify cookie settings to block third-party cookies. Firefox also currently has the ability to block third-party cookies but users have to manually enable it, it isn’t by default.

According to Jonathan Mayer, research at Stanford and the person who contributed the third-party cookie blocking code to Firefox, third-party cookie blocking in Firefox 22 is “slightly relaxed version of the Safari policy”. What does that mean in layman’s terms? I’m not really sure but I do know advertisers are about to throw a fit in 3… 2… 1…

[via ArsTechnica. Mozilla]