Did you update Firefox to 3.6.18 when the security update was issued? You can check by going to '''Help '''| '''Check For Updates'''. Update immediately if you see the option to do so. There was a security breach at a major SSL certificate provider called Comodo quite recently whereby an affiliate RA was compromised. That allowed a number of fraudulent SSL certificates to be issued. SSL is an acronym for Secured Socket Layer and means that the transmission is encrypted to prevent eavesdropping. Your banking site will use just such a certificate. Browsers are configured to accept SSL certificates from providers such as Comodo using OCSP to check authenticity. However, if a fraudulent certificate was to fall into the wrong hands, then this could be used to impersonate a site such as a banking site. In the case of the security breach which you can read about @ [http://blogs.comodo.com/it-security/data-security/the-recent-ra-compromise/ Comodo blog] Mozilla blacklisted the fraudulent certificates within 24 hours and this blacklist was released as an update to Firefox in v3.6.18 it's important to ensure you're running the latest version of the 3.6.x series to safeguard yourself if you don't want to upgrade to Firefox 4 for some reason or other. As regards your current problem, try starting Firefox in [[Safe Mode]] If it works properly in that configuration, then one of your add-ons is the cause of the problem. Also, check your plugins @ [http://www.mozilla.com/en-US/plugincheck/ Plugins Check] You may find you need to update those too.