Kaspersky Internet Security is a software package for Windows that 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 Kaspersky isn't configured correctly, it can prevent Firefox from accessing the Internet; Firefox will give Server not found errors. Even when supposedly disabled or uninstalled, it can block Firefox.

Updating Kaspersky Internet Security

You should be running the latest version of Kaspersky Internet Security. Older versions have bugs that adversely affect Firefox. Updates to Kaspersky Internet Security are free and are available on Kaspersky's website.

Configuring Kaspersky Internet Security

Kaspersky Internet Security must be configured correctly to allow Firefox access to the Internet, sometimes even when Kaspersky Internet Security's firewall is disabled. Even if Firefox worked with Kaspersky at one point, updates to Firefox can make Kaspersky treat the Firefox update like a different program.

These instructions are for Kaspersky Internet Security 7.

1. Start Firefox.
2. Right-click the Kaspersky icon in the system tray at the bottom right of the screen.
   
   
   
3. Click Settings....
4. On the left side of the screen under Protection, click Firewall.
   
   
   
5. On the right side of the screen, check mark Enable Firewall if it isn't already check marked.
6. On the right side of the screen under Filtration system, make sure the slider is not set to Block All.

• • If the filtration system is set to Block All, you will need to lower the setting to be able to use Firefox.
    
    
    

1. On the right side of the screen under Filtration system, click Settings....
   
   
   
2. Click the Rules for applications tab.
3. If there is an entry for firefox.exe, select it and click Delete.
   
   
   
4. Click Add..., select the Applications menu and choose C:\Program Files\Mozilla Firefox\firefox.exe. A window titled Edit rules for firefox.exe will appear.
5. Click Template... and choose Mozilla Firefox.
6. Click OK.
7. Click OK.
8. Click OK.
9. Open Firefox and try to access any website.

Kaspersky Internet Security should now allow Firefox access to the Internet.

Removing Kaspersky Internet Security

Simply uninstalling Kaspersky Internet Security sometimes doesn't remove it completely. Kaspersky offers a utility to completely remove Kaspersky Internet Security. It is available on Kaspersky's website.

Based on information from Firewalls (mozillaZine KB)