Looks like they have a problem again. Read artical here :
Critical flaws found in Firefox
The Mozilla Foundation has said it is "working aggressively" to fix two flaws in its open source Firefox browser.
The vulnerabilities, reported on Saturday, were identified as "very critical", but no cases had been reported of them being exploited.
Several security firms identified the flaws which could let websites run malicious code on a person's computer.
FF is still the best.