Checking for Windows XP Firewall

To see if you're running Windows Firewall:

1. Click on the Windows Start button, and select Control Panel. The Control panel window will appear.
2. Click on the Security Center link. The Security Center will appear.
3. If the Firewall header says ON, you are running Windows Firewall.

Configuring Windows XP Firewall

If you're running Windows Firewall and having connection problems in Firefox:

1. Click on the Windows Start button, and select Control Panel. The Control panel window will appear.
2. Click on the Security Center link. The Security Center will appear.
3. If the Firewall header says ON, you are running Windows Firewall.
4. Ensure that Don't allow exceptions is not selected.
5. Click to select the Exceptions tab.
6. Find Mozilla Firefox (or firefox.exe) in the list of programs. If it is there, click to select it. If not, skip the next step.
7. With Mozilla Firefox selected, click the Delete button. Confirm that you want to delete the entry.
8. Click the Add Program... button.
9. In the Add a Program window, click the Browse... button.
10. Navigate to the Firefox program directory (e.g. C:\Program Files\Mozilla Firefox\) and double-click on firefox.exe.
11. Click the OK button to close the Add a Program window.
12. Click the OK button to close the Windows Firewall Settings window.

Source:- http://support.mozilla.com/en-US/kb/Configuring+Windows+Firewall

A firewall is a device or a set of devices, which can be implemented in any of the hardware, software or both. All the messages passing through the firewall are verified to meet some level of security criteria.

It acts as a computer security barrier, which analyzes all the incoming and outgoing traffic to and from your computer or network based on the firewall settings. There are some common types of firewalls like: Application level gateway, Packet filtering firewall, Circuit gateways and Hybrid firewall.

Application level gateway firewall works on the application layer of the protocol stack. It works more intelligently than the packet filtering firewall. Packet filtering firewall examines the information contained in the header of the message packets.

There are some factors based on which the filters can be added or removed from the firewall:

1. IP address

2. Ports

3. Protocols

IP address: Every computer connected to Internet has a unique IP address. The firewall configuration can be customized to block any IP address so that your computer will not allow any kind of communication to take in between.

Ports: The firewall can be configured to allow or block messages from any port number.

Protocols: There are some commonly used protocols like IP, HTTP, TCP, FTP, and SMTP etc., which can be included in the firewall filter.

Some operating systems, such as Microsoft Windows offer built-in firewalls that are turned on by default to block all the incoming threats from Internet. There are several other third party firewalls available. You can choose any one the firewall to replace the default firewall in Windows.