You can configure Mozilla Firefox to use a proxy server to connect to the Internet. A proxy server acts as a security barrier between your internal network and the Internet, keeping others on the Internet from being able to obtain access to information that is located on your internal network.
Mozilla Firefox 2.0
1. Open Mozilla Firefox.
2. Click on Tools then click on Options….
3. Click on the Advance tab, then click on the Network sub-tab and finally on the Settings… button.
4. Tick the Manual Proxy Configuration: radio.
5. In the HTTP Proxy: box, type the IP address of the proxy server.
6. In the Port: box, type the in the port number that is used by the proxy server.
7. Click OK to close the Connection Settings window.
8. Click OK to close the Options window.
TIP: To stop using a proxy just go back to the Connection Settings window and tick the Direct connection to the Internet radio.
If you really want to keep your internet privacy using proxies in Firefox, you might want to try the SwitchProxy add-on.