Most of you that know me already know that i do very well with firefox referrals (that's why they call me the Firefox Referral KING). The key is to "sell" or endorse the product - just slapping the FF button on your website will not do much good. Check Google's help page HERE (where they use my site and MY method as an example) Another very important thing is that if your visitors arent interested in something like FF, it will be more difficult to convince them to try it. for example if they are coming to your site to learn about fast cars, you will have to try harder to get them to try FireFox.. if they're coming to your site to learn how to prevent spyware, then it would be a very easy conversion.
yes... it also depends on what is the content of your site and your user types... if it's for teenager, it's kind of hard to encourage them to buy anything from referral...
It depends on your type of site , If you have a site about online job then you can sell products or softwares about home based online job effectively , and its hard to sell products that are not related to your site.
Yeah, try to pick some stuff thats actually related to site content. or put something like: "Best displayed in FireFox" and then have the referral button