Mozilla has released updates to the Firefox 3.5 and Firefox 3 versions. These updates were aimed at some of the security problems that arose in both the new and the old versions. It’s highly recommended that Firefox users upgrade to these new updates.

If you’re using Firefox 3.5 then you can download update 3.5.3 from here 

If you’re using any older version then update to 3.0.14 from here

You will also be notified for these upgrades within 48 hours but if you want to make sure you don’t miss these updates then do it manually now by selecting “Check for Updates” from the Help menu.