Mozilla is planning to add a "do-not-track" mode to Firefox, which will allow Web users to signal that they don't want websites to track them. The only problem is that the feature will only work if companies agree to not track its users. "Mozilla recognizes the chicken and egg problem," the company's public policy leader wrote in a blog post. Last month, Microsoft announced Internet Explorer 9 browser will feature powerful privacy tools that allow users to disable tracking features. The move toward anti-tracking modes is a response to the Federal Trade Commission's call for the feature and the Obama administration's demand for a "privacy bill of rights" to protect Internet users from intrusive monitoring. Firefox receives much of its revenue through an ad partnership with Google that depends heavily on tracking Web surfers.