Google have widened the availability of the Firefox referal program to now include international publishers. They announce it as follows on their 

‘International publishers can now refer users to Firefox plus Google Toolbar through the AdSense referrals feature. As you connect your users with Firefox to improve their web browsing experience, you can generate earnings - up to US$1 for each new Firefox user who downloads and runs the product for the first time. To add a Firefox referral button to your site today, visit the ‘Referrals’ tab in your account.’

When a user downloads and installs Firefox through your referral, we'll credit your account with up to $1.00