Mozilla will automatically block third-party cookies starting with Firefox 22, which is slated to ship this summer, according to the Stanford University researcher who coded the change.

The move, which will make it more difficult for online ad networks to track users' activities, was only the latest skirmish in a war between advertisers and some browser makers.

In a blog post and on Twitter, Jonathan Mayer, a graduate student in computer science and law at Stanford University, and one of two researchers at the school who created the HTTP header implementation that signals a user's "No Dot Track" preference, announced the new Firefox cookie policy.

Mayer kick-started the change last December when he submitted code to the Bugzilla bug-tracking database operated by Mozilla. It was Mayer's first contribution to the open-source Firefox.

"The default Firefox cookie policy will, beginning with release 22, more closely reflect user privacy preferences," Mayer claimed in a post to his blog last week.

Mozilla has added the cookie change to Firefox's "Nightly" channel, the browser's roughest-edged version. Unless the modification is sidetracked or Mozilla changes its mind, the new policy will first appear in a final release of Firefox on June 25.