advocates owe a debt of gratitude to Jonathan Mayer, a grad student at Standford who developed a patch for Firefox
that, by default, blocks third-party cookies from installing on their browser, thereby protecting users from being tracked by advertisers. Mozilla
plans to bake the patch into Firefox 22, which scheduled for release in late June (the current version is Firefox 19).
To get the most out of the patch, and Firefox 22, users are encouraged to clear out all existing cookies when upgrading. The patch doesn't make any special provisions for pre-existing cookies, though it will block new ones from third-parties if the user hasn't visited the site the cookie comes from. Such cookies are used by advertisers to track users and deliver targeted ads.
Third-party advertisers users cookies to track users across the web. Image Source: Flickr (scubadive76)
This is similar to how Safari handles things, which gives permission to first-party cookies, whereby third-party content only has cookie permissions if the content already has at least one cookie set. In short, Firefox 22's handling of cookies is "a slightly relaxed version of the Safari policy," Mayer says.
There shouldn't be much collateral damage in the form of broken websites, but just to be sure, the Mozilla privacy team is "closely monitoring" things before Firefox 22 goes gold.