Absolutely not! Mozilla has no specific requirements as to which security program should be used with Firefox. If you are happy with what comes with Windows 7, keep using it. If you aren't, I think you should consider using Avira Personal Free - http://www.free-av.com/. That is my current choice and has been for that last 3 years. I have access to a free version of Norton every "back to school" sales season, and my only use for those CD's is as a frisbee-like toy.