After creating a new world record as the most downloaded application in the first day out doesn’t mean Firefox 3 has no security issue. Tippingpoint has found a very first vulnerability just five hours after the browser is released. The vulnerability allows attackers to run programs on any Firefox user’s computer. To expose the vulnerability, victims would have to click on the wrong link first.
Although this vulnerability details won’t be released to public until the Firefox developer has a chance to repair the problem, there is no waranty that nobody has found the same vulnerability. They might have created some tools to exploit this hole.