Firefox

Firefox is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. First released in November 2004, Firefox uses the Gecko rendering engine and is available for Windows, macOS, Linux, Android, and iOS. ^[1] The browser emerged from the Mozilla project, which itself originated from the 1998 release of Netscape's source code. ^[2]

Firefox reached approximately 30 percent global market share around 2009, making it the second-most-used browser worldwide at its peak. Its market share has since declined substantially, falling to approximately 2–3 percent globally as of late 2025, with somewhat higher usage on desktop platforms and in certain European markets. ^[3]

History

The origins of Firefox trace to January 1998, when Netscape Communications announced it would release the source code for its Netscape Communicator browser suite. The release created the Mozilla project, initially housed within Netscape but later spun out as an independent effort. ^[2]

On July 15, 2003, the Mozilla Foundation was established as a nonprofit organization to continue development of Mozilla software after AOL (which had acquired Netscape in 1999) significantly reduced its involvement. The foundation received initial funding and infrastructure from AOL, Mitch Kapor, Sun Microsystems, and others. ^[4]

Firefox 1.0 was released on November 9, 2004. The Mozilla Foundation described it as offering improved security, pop-up blocking, and tabbed browsing compared to the then-dominant Internet Explorer. ^[1] On August 3, 2005, the Mozilla Foundation created the Mozilla Corporation, a taxable subsidiary, to coordinate Firefox development and generate revenue through partnerships. ^[5]

In November 2017, Mozilla released Firefox Quantum (version 57), which the organization described as a major overhaul incorporating a new CSS engine called Stylo, built using the Rust programming language, and other performance improvements from Mozilla's experimental Servo project. ^[6][7]

Technical Architecture

Firefox is built on the Gecko rendering engine, which processes HTML, CSS, and other web standards to display web pages. Gecko is one of only three major browser engines in widespread use, alongside WebKit (used by Safari) and Blink (used by Chrome, Edge, and most other browsers). ^[8]

The browser uses the SpiderMonkey JavaScript engine and has incorporated components from Mozilla's Servo research project, including the Stylo CSS engine introduced in Firefox Quantum. ^[7]

Features

Firefox includes privacy features such as Enhanced Tracking Protection, which blocks third-party tracking cookies by default, and fingerprinting defenses that limit techniques websites can use to identify users across sites. In November 2025, Mozilla announced expanded fingerprinting protections intended to make Firefox more resistant to tracking techniques that do not rely on cookies. ^[9]

The browser supports extensions through the WebExtensions API, which provides cross-browser compatibility with extensions written for Chrome and other browsers. ^[10]

Organization and Funding

Firefox is developed by the Mozilla Corporation, a taxable subsidiary of the nonprofit Mozilla Foundation. The foundation was established in 2003, and the corporation was created in 2005 to handle commercial activities. ^[4][5]

Mozilla's revenue comes primarily from search engine partnerships, under which search providers pay to be the default search option in Firefox. According to Mozilla's 2024 annual report covering fiscal year 2023, total revenue was approximately $653 million, with roughly $495 million (about 76 percent) coming from search partnerships. Google accounts for the majority of this search revenue. ^[11][12]

This financial structure has drawn attention because it makes Mozilla substantially dependent on revenue from Google, which also develops Chrome, Firefox's primary competitor. Mozilla has acknowledged this dependency and has pursued diversification through products including Mozilla VPN, the Mozilla.ai subsidiary, and advertising services. ^[11][13]

Market Position

Firefox's global market share has declined from approximately 30 percent at its peak around 2009 to roughly 2–3 percent as of late 2025. Desktop market share is somewhat higher, estimated at around 6 percent, while mobile market share is below 1 percent. Usage varies by region, with stronger presence in some European markets including Germany, where desktop share is estimated at approximately 10 percent. ^[3]

The browser's decline coincided with the rise of Google Chrome, which launched in 2008 and became the dominant browser by the mid-2010s. Firefox remains one of the few browsers not based on Google's Chromium platform, maintaining the independent Gecko engine.

Controversies and Criticism

Mozilla has faced criticism on several fronts in recent years.

In February 2025, Mozilla introduced new Terms of Use for Firefox that included language granting Mozilla broad rights over data users transmit through the browser. The language prompted backlash from users and privacy advocates who interpreted it as potentially allowing data collection for AI training or other purposes inconsistent with Firefox's privacy-focused reputation. Mozilla responded that the terms were not intended to grant new data collection rights and subsequently rewrote the terms in March 2025 to address concerns. ^[14][15]

Mozilla's plans to integrate AI features into Firefox have also generated user concerns. In late 2025, following criticism of AI integration plans, Mozilla announced it would provide a setting allowing users to disable all AI features in the browser. ^[16]

The organization's heavy financial dependence on Google—estimated at 85 percent or more of total revenue—has been a persistent concern, as it ties Mozilla's sustainability to a competitor that has commercial incentives to see Firefox's market share decline. ^[13][12]