Howto Set Proxy at Mozilla Firefox

Firstly click at the upper left corner of the Firefox as show below

Then choose Options. When you click option, the following will be displayed.

Click on the Advance tab.

Choose Network tab and click Settings.The following will be displayed after you click the Settings

Finally put the IP Address of the proxy at the HTTP Proxy field and the port number at the Port field as shown at the picture above and then click OK. Now you can use your Firefox with the proxy enabled to browse the web. Good Luck !