Update: Mozilla has fixed the issue and released an updated version, Firefox 16.0.1. Users will be updated to the new version automatically. The Firefox download page is also showing the new version 16.0.1.
Mozilla released Firefox 16 on Tuesday and after one day it pulled from the download page due to a security vulnerability found on the build. Finding security vulnerabilities in browsers after they are publicly released is not new, in those cases vendors will simply issue fixes and patches, Mozilla has don’t this before. Firefox 16 fixes several issues found in Firefox 15.
But this time Mozilla pulled Firefox 16 build entirely and now the download page is pointing to Firefox 15.0.1. This shows the severity of the security vulnerability found. Mozilla is tight lipped on the vulnerability, but it said that this vulnerability is not yet exploited in the wild.
The vulnerability could allow a malicious site to potentially determine which websites users have visited and have access to the URL or URL parameters. At this time we have no indication that this vulnerability is currently being exploited in the wild.
The security patch might be released today, in the mean time users can use a secondary browser like Google Chrome. Alternatively Mozilla suggests to downgrade Firefox from 16 to 15, all you have to do is download Firefox 15 and reinstall it, that will replace 16 with 15.