As we already discussed about new Firefox 16.0 released a day earlier, But soon after release Mozilla realized that there is a serious security vulnerability, . Mozilla taken down the Firefox 16.0 page and Mozilla site reverted to Firefox 15.0.1. Now the patched Firefox 16.0.1 is available on mozilla FTP servers. The site is not yet updated to reflect it.
The Mozilla blog says…
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.