In a blog post, Firefox's parent company Mozilla Inc. said the tool will be called "Do Not Track." It did not say when it would be available.
As the first of many steps, we are proposing a feature that allows users to set a browser preference that will broadcast their desire to opt-out of third party, advertising-based tracking by transmitting a Do Not Track HTTP header with every click or page view in Firefox.
Microsoft's next version will also include a similar feature, though people will have to create or find their own lists of sites they want to block.
Google Chrome users can already download a plug-in that blocks advertisers, but it only works for ads that already let people opt out of targeted ads.