The bulk of Mozilla's income comes from search engine relationships, with the remainder coming from a combination of contributions, Mozilla Store sales, interest income and other sources. Compared to earlier years this is a huge jump in revenue. In 2003 and 2004 Mozilla had a revenue of $2.4 million and $5.8 million, respectively.
The big growth in revenue came after they launched Firefox in November 2004. One of the ways how Mozilla makes so much with Firefox is the built-in Google search bar in Firefox. Everytime a user searches and clicks on an ad Google pays Mozilla a small fee.
The combined expenses of the Mozilla Foundation and Corporation were approximately $8.2M in 2005, of which approximately $3M was associated with the Foundation. By far the biggest portion of these expenses went to support the large and growing group of people dedicated to creating and promoting Firefox, Thunderbird, and other Mozilla open source products and technologies. The rate of expenses increased over the year as new employees came on board. The unspent revenue provides a reserve fund that allows the Mozilla Foundation flexibility and long term stability.