Not sure a lot of referrals state you cannot tell people to click on the banners, but you can give a review of firefox and under the banner put some like "for more details" But, still I think you are ok.
You cannot say to your visitors, click on my ads. But you can write a recommendation about Firefox without saying click to download or something like that. Then your user will click automatically.
you cannot tell your visitors to click on he ads, it against TOS and will result in getting your acount banned
Incentive = give $ or something for click... Try consulting google's TOS, I would explain that stuff as Yes, you can encourage users to get ref products (that = click ref ad) BUT not the ppc ads...