McAfee a couple of years ago and no problems since should put you in the clear - however do you remember following instuctions in the NSS FAQ's @ Comcast for the insital installof Norton - in other words, remove McAfee via Control Panel and then run the McAfee Removal Tool ?
Since it has been a couple of years,I would guess it isn't necessary - but your can go ahead and run the McAfee Removal Tool to be on the safe side. You will just have to skip those steps which ask you to remove via Control Panel - also you may receive an error when it finishes running, but since you are not reinstalling McAfee you do not need to worry about it.
Any questions - ask before doing. 