Download Tor software from this link http://www.torproject.org/download.html.en

then
Install it.

Now download TOR plugin for ur FIREFOX

https://addons.mozilla.org/en-US/firefox/addon/2275

As soon as you apply that plugin , it will ask you to restart FIREFOX, do it..

Now u can see TOR DISABLED or TOR ENABLED text on right - bottom side of ur firefox browser.

Click on It if it is stating that TOR DISABLED , ur click will make it ENABLE.

Visit any IP showing sites. and check ur ip address.

Its all done