Note that $15 million is nowhere near enough to pay the number of employees who work on Firefox. As a for-profit (unlike the foundation), Mozilla the corporation has to pay folks market rates, and if you're paying an employee in the US, you're paying that same amount on top as taxes, insurance, benefits, etc. etc. so $15 million gets you a few dozen people at most. Mozilla employs a few hundred. So you'll have to add a zero to that number before it's in the same ballpark (e.g. wikipedia would be a good example).