Mozilla has released an update to Firefox 3.5 as version 3.5.6. The new update fixes several security issues including 3 critical issues and 4 other medium and less critical ones. In addition to that, Firefox 3.5.6 also addresses several stability issues with the browser.
In all around 62 bugs were fixed in this version. Right now Firefox is not forcing an update on users, so you will have to manually update Firefox on your own. You can always refer to our tutorial on How to manually update Firefox.