The Mozilla Foundation is a non-profit organization that exists to support and collectively lead the open source Mozilla project. Founded in July 2003, the organization sets the policies that govern development, operates key infrastructure and controls Mozillatrademarks and copyrights. It owns a taxable subsidiary: the Mozilla Corporation, which employs many Mozilla developers and coordinates releases of the Mozilla Firefox web browser and Mozilla Thunderbird email client. The subsidiary is 100% owned by the parent, and therefore follows the same non-profit principles. The Mozilla Foundation was founded by the Netscape-affiliated Mozilla Organization. The organization is currently based in the Silicon Valley city of Mountain View, California, United States.

Firefox 3.0 uses version 1.9 of the Gecko layout engine for displaying web pages. This version fixes many bugs, improves standards compliance, and implements many new web APIs compared to Firefox 2.0. Other new features include a redesigned download manager, a new "Places" system for storing bookmarks and history, and separate themes for different operating systems.

Firefox 3.0 had over 8 million unique downloads the day it was released, and by July 2008 held over 5.6% of the recordedusage share of web browsers.^[2] Estimates of Firefox 3.0's global market share as of February 2010 were generally in the range of 4–5%,^[3][4][5] and then dropped as users migrated to Firefox 3.5 and later Firefox 3.6. Partially as a result of this, between mid-December 2009 and the end of January 2010, Firefox 3.5 was the most popular browser (when counting individual browser versions) passing Internet Explorer 7.^[6]

Mozilla ended support for Firefox 3 on March 30, 2010 with the release of 3.0.19.

The Mozilla Foundation will ultimately control the activities of the Mozilla Corporation and will retain its 100 percent ownership of the new subsidiary. Any profits made by the Mozilla Corporation will be invested back into the Mozilla project. There will be no shareholders, no stock options will be issued and no dividends will be paid. The Mozilla Corporation will not be floating on the stock market and it will be impossible for any company to take over or buy a stake in the subsidiary. The Mozilla Foundation will continue to own the Mozilla trademarks and other intellectual property and will license them to the Mozilla Corporation. The Foundation will also continue to govern the source code repository and control who is allowed to check in.

The Mozilla Foundation describes itself as "a non-profit organization that promotes openness, innovation and participation on the Internet."^[2] The Mozilla Foundation is guided by the Mozilla Manifesto, which lists 10 principles which Mozilla believes "are critical for the Internet to continue to benefit the public good as well as commercial aspects of life".

On August 3, 2005, the Mozilla Foundation announced the creation of Mozilla Corporation, described as "a taxable subsidiary that serves the non-profit, public benefit goals of its parent, the Mozilla Foundation, and that will be responsible for product development, marketingand distribution of Mozilla products."^[6] It also handles relationships with businesses, many of which generate income. Unlike the Mozilla Foundation, the Mozilla Corporation is a tax-paying entity, which gives it much greater freedom in the revenue and business activities it can pursue. From 2004 to 2014, the majority of revenue came from a deal with Google Inc., which was the default search engine in the Firefox web browser. In November 2014, Mozilla signed a five-year partnership with Yahoo,^[7] making Yahoo Search the default search experience for Firefox in the U.S. Yandex Search is the default for Firefox in Russia and Baidu continues its role as the default in China.