How to fake the X-Forwarded-For (XFF) HTTP header

http://addons.mozilla.org/en-US/firefox/addon/967 then:

1) In Firefox, Go to tools->modify headers

2) From the drop down box on the left select add

3) Then enter: "X-Forwarded-For" in the first input box without the quotation marks

4) Enter: "12.13.14.15" in the second input box without the quotation marks

5) Leave the last input box empty, and save the filter, and enable it
http://imgur.com/Feb4.png

6) Click the 'Configuration' tab on the right then proceed to check the 'always on' button.

Close the Modify Headers box and it should work.
Works for TheDailyShow.com, southparkstudios.com, and ColbertNation.com