Mozilla Firefox Proxy configuration

Step 1.
Find a list of free proxy. One such list is here.

Step 2.
Now choose an IP address and port from this list. In this tutorial I have chosen IP: 195.175.37.6 and port: 8080. You can choose whatever you like.

Step 3.
Open Firefox and in the menu choose Tools and then Options.


This will open the Firefox Options window. Click on Advance Options.


Step 4.
Click on Network tab and the click Settings button under Connection.


Step 5.
In Connection Settings window, click Manual proxy configuration. Now enter the IP address in HTTP Proxy and Port address in Port (in this example HTTP Proxy address is 195.175.37.6 and Port is 8080).
Also check the box 'Use this proxy server for all protocols'.


Click ok and your IP is set to desired Proxy.

You can use any online service to check your IP. Like check my IP is a site solely dedicated for this purpose.