Fraudulent SSL Certificate has been issued by Root Certificate authority, DigiNotar against Google users in Iran, both Google and Mozilla are aware of this. This fraudulent certificate can be used to spoof web content, perform phishing attacks or perform man-in-middle attacks against end users. To protect users from this, Google released update for Chrome browser as Mozilla today released Firefox 6.0.1 security update which revokes this certificate and Microsoft also released Security advisory .
To update your Firefox browser
From Firefox button>Select “Help” menu and click “About Firefox” to let Firefox download and restart the browser to install the update.