From the ‘Free Software Making $$’ files:
Mozilla gives its software away for free, yet year after year they keep making money. For the 2008 year, Mozilla is just now disclosing how much revenue it generated and it was another growth year for the open source group.
Revenue at Mozilla was reported at $78.6 for 2008 which is a 5 percent increase over the $75.1 million reported in 2007. The revenue growth rate appears to have slowed somewhat in my opinion. Back in 2005, Mozilla’s revenues were only $53 million.
As has been the case over the last several year the bulk of Mozilla’s revenue is driven by search revenues generated from Firefox by Google, Yahoo, Amazon and eBay. So whenever you search using the default start page in Firefox, you’re actually helping to support Mozilla.