So, can "Google and FireFox Ad" be categorized under referrals ?
Might help if you link to the user in question - there IS a mod available however that is technically legal because it's not actually a user posting it. It runs on several forums, maybe x10 put it in - usually right after the first post, a bot user named something like "Sponsored Ads" posts with the ad-code to make ads show up.
If thats the kind you're talking about then that's not anything you can really stop cause it's not actually a user, and the mod was installed to do it. If it's a user, then its probably up for review, but without seeing it in action we can't really see what you're speaking about, know what I mean?