Ive read this story at Digg http://digg.com/deals/Site_offers_half_of_ad_revenue_for_Firefox_downloads bonemicrosoft dot com offers 0.50$ for each firefox download... Firefox Revenue Share -we'll send you $.50 for ditching Microsoft's awful attempt at taking over the web.
That's a good way to get people to download it, but just like jbw said, there's probably no way to track it. On top of that, giving an incentive to users is probably against Google AdSense's TOS as it is to ask users to click on ads. I cannot confirm this, but I would assume it would be against the TOS.
Google offers a dollar for a firefox download. They also incorporated their Google toolbar into the download.
thats what they make u to believe (if u read more carefully they say up to $1 ) its more like $0.40-$0.35