To fix a security vulnerability in the previous release, Firefox developers have issued an early follow-up version 3.6.2 for immediate implementation.
The release was originally planned for March 30, but the urgency of the fix for the multiple vulnerability gave the Firefox update a priority for an earlier availability.
Firefox 3.6 users will get the fix update via the built-in mechanism over the next 24 to 48 hours. Linux distros will also be distributing new packages. Updates are also recommended for versions 3 and 3.5 users, who can download 3.6.2 from their browsers. The release notes provide further details.