Mozilla has released updates for Firefox 3.5 and 3.6. These updates blacklist a few invalid HTTPS certificates [additional details]. If you have not already been prompted about this update you can get the update manually by going to Help Menu then Check For Updates…
UPDATE to Firefox 4. 0– After installing the updates and restarting you will be presented with one of the below announcements that Firefox 4.0 is available and a Download now! button to download. Note: If you do no get these screens, your system does not meet the requirements for Firefox 4.
If you want to upgrade to Firefox 4.0 DO NOT click this button, instead go to the Help Menu then select Check For Updates… again and you will be presented with an update to Firefox 4.0: