Firefox browser will offer to block web tracking Mozilla, the non-profit group that created the Firefox web browser, has said it plans to allow its 450 million users to block the internet tracking that allows third parties to monitor their movements online. When the plans were first mooted in February, one advertising executive reportedly described them as "a nuclear first strike" against the advertising industry. Tracking allows firms to follow a user's tastes and target them with appropriate online ads. However, the blocking technology would arrive just as users in the US and worldwide are becoming increasingly concerned about the level of access companies are allowed to their data and browsing habits - especially following the recent revelations that several of those companies have passed such data on to the National Security Agency for intelligence-gathering purposes. The new technology would restrict so-called "cookies": small files attached to the browsers of individual users by data collection outfits, allowing them to keep track of that user's web behaviour long after the end of their latest online session. In future, such tracking would only occur if the user gives permission to specific websites that he or she visits regularly, such as social networks, news and shopping sites. They would have an option to block cookies from sites visited infrequently or unintentionally, and to limit the level of tracking by sites such as Facebook once they sign off and navigate elsewhere. The free, open source Firefox browser is used by approximately 20 per cent of desktop computers globally, making it the world's third most popular browser after Google's Chrome and Microsoft's Internet Explorer. The new blocking tools owe much to Apple's Safari browser, which already blocks cookies from sites that users do not visit on purpose. Brendan Eich, chief technology officer for Mozilla, told the Washington Post, "We're trying to change the dynamic so that trackers behave better." Most users will not have access to the tools, which are still being developed, for another few months. Meanwhile, Mozilla has partnered with Stanford University's Centre for Internet and Society and the makers of the Opera browser, to draw up a "Cookie Clearinghouse": a definitive list of those websites to be to be allowed to place cookies in users' browsers, and those to be automatically blocked.