I do not use referals, I have better results with text links, I guess it's because of my location (Morocco) and my site topic (classifieds).
It depends on your site topic. If you have a site about weddings, for example, I doubt you'd make a whole lot using a Firefox referral. Also, you can promote your referrals to a certain degree. I myself haven't used referrals a lot, since they've never worked out that well for me.