Firefox has unpatched "extremely critical" security holes and exploit code is already circulating on the Net, security researchers have warned.
The two unpatched flaws in the Mozilla browser could allow an attacker to take control of your system.
The flaws were confidentially reported to the Foundation on 2 May, but by Saturday details had been leaked and were reported by several security organisations, including the French Security Incident Response Team (FrSIRT). Danish security firm Secunia marked the exploit as "extremely critical", its most serious rating, the first time it has given a Firefox flaw this rating.
In recent months Firefox has gained significant market share from Microsoft's Internet Explorer, partly because it is considered less vulnerable to attacks. However, industry observers have long warned that the browser is more secure partly because of its relatively small user base. As Firefox's profile grows, attackers will increasingly target the browser.
Mozilla Foundation said it has protected most users from the exploit by altering the software installation mechanism on its two whitelisted sites. However, users may be vulnerable if they have added other sites to the whitelist, it warned.
"We believe this means that users who have not added any additional sites to their software installation whitelist are no longer at risk," Mozilla Foundation said in a statement published on Mozillazine.org.