The F-Secure Internet Security software package for Windows includes a firewall component, which controls the programs that can connect to the outside world and the types of connections that they can make. If F-Secure Internet Security doesn't permit Firefox to connect to the Internet, Firefox may generate a Server Not Found - Troubleshoot connection problems error when you try to browse to websites.
These instructions are written for F-Secure Internet Security 2008. Other versions of F-Secure Internet Security may require a different procedure
At the top of the Firefox window, click the File menu, and select Exit.
Click the Windows Start button, then click All Programs > F-Secure Internet Security 2008> Open F-Secure Internet Security 2008 to launch the F-Secure Internet Security 2008 window.
On the left side of the F-Secure Internet Security 2008 window, click on the Internet Shield icon.
Next to Firewall, click the Configure... link. The Firewall window will appear.
On the left side of the Firewall window, click Application Control to display the list of applications.
Find Firefox or firefox.exe in the list and click on it to select it. Then click Remove... to remove it from the list.
Click Add... to bring up the Application Properties window.
In the Application Properties window, click Browse... to bring up the Open window.
In the Open window, navigate to the Firefox installation folder. By default it is C:\Program Files\Mozilla Firefox\. Double-click on firefox.exe.
In the Application Properties Window, change both Outbound (client) connection and Inbound (server) connection to Allow.
Click OK to close the Application Properties Window.
Click OK to close the Application Control Window.
Click the X in the top-right corner of the F-Secure Internet Security 2008 window to close it.