I'm pretty sure we don't get anywhere near a billion dollars from Google. I haven't paid attention to our financials in a while, but the most recent public financial documents from 2011 say "Mozilla’s consolidated reported revenue (Mozilla Foundation and all subsidiaries) for 2011 was $163M (US), up approximately 33 percent from $123M in 2010."
A billion dollars over three years is a bit different. That may be the number, I have no extra information here. It may also be made up, I don't really see any useful sources.
http://www.mozilla.org/en-US/foundation/annualreport/2011/fa...