Firefox 16 was released just a day ago by Mozilla and was available for download from the Mozilla Public Servers. But today Mozilla pulled out Firefox 16 from their servers after a Security Vulnerability was discovered in Firefox 16. They are working on a fix and plan to ship updates tomorrow. At the moment, Firefox 16 is temporarily removed from the current installer page and  you can only download Firefox 15.0.1 from their servers.

Details of Security Vulnerability discovered

The vulnerability discovered could allow a malicious site to potentially determine which websites  users have visited and have access to details like URL or URL parameters. Mozilla is still to receive any reports about the vulnerability being exploited by hackers.

Downgrade to Firefox 15.0.1

If you have already downloaded and installed Firefox 16, its better you switch to Firefox 15.0.1.  If you don’t want to downgrade to Firefox 15, you can wait for the patch to arrive. Firefox 16 will be updated automatically when Mozilla releases the patch for Security Vulnerability.

via: Mozilla Blog