Mozilla identified and fixed several memory safety bugs in its browser engine used in Firefox 3.6, Firefox 5 and other Mozilla-based products. Some of these bugs showed evidence of memory corruption under certain circumstances, and that they fear that someone with enough effort could be exploited to run arbitrary code. This update is considered CRITICAL by Mozilla.
As with most updates, I strongly recommend that all Firefox users upgrade to these releases. If you already have Firefox, you will receive an automated update notification within 24 to 48 hours.
For a list of changes and more information, please review the Firefox release notes at: