Comodo Firewall Pro is a freeware software package for Windows that that controls the programs that can connect to the outside world and the types of connections that they can make. If Comodo Firewall isn't configured correctly, it can prevent Firefox from accessing the Internet, causing Firefox to give Server Not Found - Troubleshoot connection problems errors. This article describes how to configure Comodo Firewall Pro to give Firefox access to the Internet.
Open Comodo Firewall Pro - click the Windows Start button, then click All Programs > Comodo > Firewall > COMODO Firewall Pro.
In the Summary window, under the Security Monitoring heading, click the Application Monitor.
In the list of Application Control Rules, locate any mentions of Firefox or firefox.exe. Click on each one, then click Remove.
After removing each instance of Firefox in the Application Control Rules list, click the Tasks button.
In the Tasks window, click the Define a new Trusted Application.
In the Trusted Application window, under the Specify Application heading, click Browse... Navigate to your Firefox program folder (usually C:\Program Files\Mozilla Firefox\ and choose firefox.exe. Click OK at the bottom of the Trusted Application Window.
Return to the Application Monitor by clicking its icon on the left side of the Window. You should see Firefox listed, this time with full access rights.