Firefox

Mozilla Firefox, or simply Firefox, is a free and open-source web browser made by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to show web pages, and it follows current web standards. Firefox works on Windows, macOS, and Linux. There is also a mobile version for Android (see Firefox for Android) and iOS. Unofficial versions exist for other systems, such as Oracle Solaris and OpenIndiana.

Firefox is the spiritual successor of Netscape Navigator. Netscape created the Mozilla community in 1998, before AOL bought Netscape. In 2002, members of the Mozilla community made Firefox, which had the codename "Phoenix." They wanted a separate browser, not the Mozilla Application Suite bundle. During its beta phase, testers liked its speed, security, and add-ons. They compared it to Microsoft's Internet Explorer 6, which was then the most used browser. Firefox was released on November 9, 2004. It challenged Internet Explorer's popularity by reaching 60 million downloads within nine months. In November 2017, Firefox began using new technology called "Quantum." This was meant to encourage parallelism and a more easy-to-use user interface.

The current version of Firefox works on Windows 10 or later versions of Windows, as well as on macOS and Linux. Unofficial versions are available for several Unix systems, such as Oracle Solaris and OpenIndiana. They also work on Unix-like systems, including FreeBSD, OpenBSD, NetBSD, and ReactOS. Firefox is the default browser on Debian, Ubuntu, and some other Linux versions. It is also available for Android and iOS. However, the iOS version uses the WebKit layout engine instead of Gecko, because iOS requires it. An optimized version was once available on the Amazon Fire TV. There, it was one of two main browsers, along with Amazon's Silk Browser. Firefox stopped being offered on that platform on April 30, 2021.

Firefox's usage share grew to a peak of 32.21% in November 2009. That was when Firefox 3.5 passed Internet Explorer 7. It did not pass all versions of Internet Explorer combined. Its usage later fell as Google Chrome became more popular. As of July 2026, according to StatCounter, Firefox had a 6.3% usage share on regular computers. That made it the third most popular PC browser, after Google Chrome (72%) and Microsoft Edge (10%). It was ahead of Safari (5.2%).

Main article: List of Firefox features

On computers, Firefox offers tabbed browsing, full-screen mode, spell checking, incremental search, smart bookmarks, and drag and drop for bookmarks and downloads. It also has a download manager, user profile management, private browsing, bookmark tags, bookmark exporting, offline mode, a screenshot tool, web development tools, and a settings menu at about:config for power users. Location-aware browsing ("geolocation") uses a Google service. Firefox's search uses Google by default in most markets, but other search engines can be chosen. DNS over HTTPS is another feature, and its default depends on location. Developers can use tools like the DOM Inspector and extensions such as Firebug. Firefox Hello, added in October 2014, let people make video calls using WebRTC and share files (file sharing). It was scheduled to be removed in September 2016. Some older features, such as an File Transfer Protocol (FTP) client and a 3D page inspector, are no longer part of Firefox.

Extra features called add-ons are made by third-party developers. They are mostly coded with HTML, CSS, and JavaScript. They use WebExtensions, which works with Google Chrome and Microsoft Edge extensions. Older add-ons that used XUL and XPCOM are no longer supported from Firefox 57 "Quantum" on. In 2017, an extension promoting the show Mr. Robot was added in an update without users' permission. Users can also add themes to change how the browser looks. Firefox includes dark, light, and system themes.

Firefox follows many web standards, including HTML, XML, XHTML, MathML, SVG 1.1, CSS, ECMAScript, XSLT, XPath, and APNG images with alpha transparency. It also supports some ideas from the WHATWG, such as the canvas element. Firefox 4 was the first version with major HTML5 and CSS3 support. It has passed the Acid2 test since version 3.0. Firefox 4 and later scored 100/100 on Acid3 after its SVG font tests were removed in 2011. Firefox also uses "Safe Browsing," a proprietary protocol from Google. It helps protect against phishing and malware.

Since version 38, Firefox has played videos protected by HTML5 Encrypted Media Extensions (EME). Adobe Primetime's DRM module, from Adobe Systems, runs in a sandbox. The sandbox limits its access to the computer. It also gives the module a random device ID, so services cannot easily identify the device. Since version 47, Firefox has also supported Google's Widevine module on Windows and Mac OS X. Mozilla said this was "an important step on Mozilla's roadmap to remove NPAPI plugin support." The Free Software Foundation and Cory Doctorow criticized Mozilla's decision to support EME. Since September 1, 2026, the Smart Window AI assistant is in Firefox 155.0 for users in the USA, Canada, and France.

History

See also: Firefox version history

The project began as an experimental branch of the Mozilla project. Its creators were Dave Hyatt, Joe Hewitt, and Blake Ross. They felt that business needs and many added features had made the Mozilla browser heavy and slow. To fix the software bloat they saw in the Mozilla Suite, they built a separate browser meant to replace it. Version 0.1, named Phoenix, was released on September 23, 2002. On April 3, 2003, the Mozilla Organization said it would focus on Firefox and Thunderbird instead of the Mozilla Suite.

The browser has had several names. It was first called Phoenix, after the mythical bird that rises from the ashes. This was a nod to its predecessor, Netscape Navigator, which had lost ground to Microsoft Internet Explorer during the "First Browser War." In 2003, it was renamed after a trademark claim from Phoenix Technologies. The next name, Firebird, caused objections from the Firebird database software project. For a time, the browser was called Mozilla Firebird. On February 9, 2004, it became Mozilla Firefox. The name was said to come from a nickname of the red panda, which became the project's mascot. Mozilla prefers the short forms Fx or fx, though FF or Ff are often used.

Firefox became popular with news outlets such as Forbes and The Wall Street Journal before version 1.0. Its popular features included a built-in pop-up blocker, tabbed browsing, and a way to add extra functions. Other browsers, such as the Mozilla Suite and Opera, already had these features. Firefox was different because it quickly gained a large number of users. It became a popular choice over Internet Explorer, which critics said had poor design and weak security. Microsoft responded by releasing Windows XP Service Pack 2, which added security features to Internet Explorer 6. Version 1.0 was released on November 9, 2004, and many more versions followed. From version 5 onward, new versions came out much more quickly. By the end of 2012, the stable release had reached version 17.

In 2016, Mozilla announced a project called Quantum. It aimed to improve the Gecko engine and other parts of the browser so it would run faster and feel more modern. The browser also moved to a multi-process model. This came after Firefox lost users to Google Chrome and after people said it was slower. Because of these changes, older add-ons no longer worked, and a new extension system was introduced. Firefox 57, released in November 2017, was the first version to include Quantum improvements. By default, Firefox spreads tabs across four processes, which helps balance memory use and speed.

Firefox for Android added a guest session mode in 2013. It cleared browsing data at the end of each session. This feature was removed in 2019. In May 2019, an expired certificate on Mozilla's servers caused Firefox to turn off all add-ons. A fix was released soon after. Firefox ended support for Adobe Flash in January 2021. In June 2021, a new design called 'Proton' was released to all users, and some people did not like it. In September 2023, Firefox 118.0 added the ability to translate web pages on the device itself, based on the work of Project Bergamot. In January 2024, Mozilla also introduced an official APT repository for Debian-based Linux distributions.

Security

See also: Browser security

Firefox was made to be a safe browser from the start. At that time, Internet Explorer was the most popular browser, but it had many security problems. malware like Download.Ject could be installed just by visiting a harmful website. The U.S. government reportedly warned people about these risks. Firefox was less connected to the computer's operating system, so it was seen as a safer choice. This helped it become much more popular in the early 2000s. In 2006, The Washington Post reported that known problems in Internet Explorer stayed open for 284 days, while Firefox's stayed open for only nine days. A Symantec study found that Firefox had more security vulnerabilities, but its problems were usually fixed faster than in other browsers.

Early Firefox ran all of its parts together in one monolithic architecture. This meant that a problem in one part could affect the whole browser. Most browsers moved to a safer design between 2008 and 2012, but Firefox changed later. Its Electrolysis (e10s) project began in 2015. The new version was released in beta in 2016 and turned on for all users in November 2017. In 2012, Mozilla started Servo, an experimental browser engine. It is written in Rust and uses memory-safe methods. In 2018, parts of Servo were added to the Gecko engine in the Quantum project. This made the browser faster, more stable, and more secure. In 2020, Mozilla ended the Servo team and passed the project to the Linux Foundation. In 2026, Mozilla worked with Anthropic and used Claude Opus 4.6 to find 22 vulnerabilities in Firefox in two weeks. These were quickly fixed.

When Firefox was first released, it let scripts signed by a web page gain extra powers, such as changing a user's settings. Few websites used this, so Firefox later stopped it. Today, Firefox follows the same-origin policy used by most modern browsers. This stops scripts from reaching private data, including data from other websites. Firefox uses TLS and strong cryptography to protect information sent to websites that use HTTPS. The HTTPS Everywhere add-on, which switches a plain URL to the secure version, is now built into the browser. In 2013, Firefox planned to block third-party cookies by default. This was delayed so Mozilla could study the effects. Mozilla worked with Stanford University's "Cookie Clearinghouse" project to create a blacklist and whitelist of sites for the filter.

In version 23, Firefox blocked some content from unsecure servers on secure pages by default. JavaScript could no longer be turned off in the settings, because most websites use it. Firefox noted that extensions like NoScript were widely available for controlling it. Starting with Firefox 48, all extensions had to be signed by Mozilla and submitted to Mozilla Add-ons. Since version 60, Firefox can send DNS lookup requests in encrypted form using DNS over HTTPS. Users can set this up in about:config, and the Cloudflare servers can be used for it. In 2019, Firefox gained the ability to block scripts that used a computer's CPU to mine cryptocurrency without permission. It could also block known fingerprinting scripts that track users across the web. In 2021, Firefox added Total Cookie Protection. This helps guard against cross-site tracking by giving each website its own "cookie jar." Popular Science named this feature one of 2021's best security innovations. It was turned on by default in 2022.

Localizations

Firefox is localized, which means it has been changed to work in many languages. Mozilla uses its own Pontoon platform to do this work. When Firefox was first released in November 2004, it was available in 24 languages and for 28 locales. In 2019, Mozilla released Project Fluent, a system that gives translators more freedom. They do not have to translate every piece of text exactly word for word.

As of October 2026, the supported versions of Firefox are available in 97 locales, which cover 88 languages.

Platform availability

Desktop versions of Firefox work on Microsoft Windows, macOS, and Linux. Firefox for Android works on Android, and Firefox for iOS works on iOS. Some phones that support Linux but not Android or iOS can also run the desktop version. Examples include postmarketOS, Mobian and Ubuntu Touch. Firefox 1.0 was released for Windows 95 and Windows NT 4.0 or later. In March 2017, Firefox 52 ESR was released. It was the last version for Windows XP and Windows Vista. In November 2021, Mozilla made Firefox available on the Microsoft Store. Firefox for Linux has worked on 32-bit computers since the beginning. 64-bit versions came with the 4.0 release.

The mobile version of Firefox, code-named "Fennec", was first released for Maemo in January 2010. It came to Android in March 2011. In August 2020, Mozilla launched a new Android app called Firefox Daylight, codenamed Fenix. At first, Mozilla did not want to bring Firefox to iOS. Apple had rules that limited third-party browsers on iOS. In 2015, Mozilla decided to go ahead with Firefox for iOS. It was fully released in November of that year. Firefox Reality was released for augmented reality and virtual reality headsets in September 2018. Firefox has also been adapted for FreeBSD, OpenBSD, and OpenIndiana, among other systems.

Channels and release schedule

In March 2011, Mozilla shared plans to switch to the rapid release model. This meant a faster 16-week development cycle, similar to Google Chrome. Ars Technica noted that this brought "significant technical and operational challenges," such as keeping add-on programs working. However, it would help Firefox adopt new web standards, features, and speed improvements sooner. The plan started in April 2011. Releases moved through four "channels," with each stage taking about six to eight weeks. They started with an early test version in the Nightly channel and ended with the public release channel. For businesses, Mozilla added an Extended Support Release (ESR) channel, with new versions every 30 weeks. Mozilla warned that this channel was less secure than the release channel. Security fixes were only backported for the most serious problems.

In 2017, Mozilla dropped the Aurora channel, which had few users. It also rebased Firefox Developer Edition onto the beta channel. Mozilla uses A/B testing and a staged rollout for the release channel. Updates first reach a small group of users. Mozilla watches for crashes or other problems before sharing the update with everyone. In 2020, Firefox moved to a four-week release cycle to keep up with Chrome's support for new web features. Chrome switched to a four-week cycle a year later. On September 1, 2026, Firefox moved to a two-week cycle.

Licensing

Firefox source code is free software. Most of it is released under the Mozilla Public License (MPL) version 2.0. This license lets anyone look at, change, or share the code. Because of this, other programs have been built from it. These include Firefox's predecessor Netscape, the customizable Pale Moon, and the privacy-focused Tor Browser.

Firefox was once licensed only under MPL 1.1. The Free Software Foundation said this license was weak copyleft. It allowed some derivative works to be kept private. MPL 1.1 code also could not legally be combined with code under the GPL. To fix these concerns, Mozilla re-licensed most of Firefox under a tri-license scheme. Developers could choose MPL 1.1, GPL 2.0, or LGPL 2.1, whichever suited them. Mozilla then released MPL 2.0, which works with the GPL, on January 3, 2012. With the release of Firefox 13 on June 5, 2012, Mozilla used MPL 2.0 in place of the tri-licensing scheme.

Logo and visual identity

The Firefox icon is a trademark. Only the official Mozilla version of Firefox and versions made by official partners can use it. Companies that change Firefox cannot use it.

Early versions of Firefox looked fine, but they were not as polished as many professional programs. In October 2003, designer Steven Garrity wrote an article about what he thought was wrong with Mozilla's look. Soon after, Mozilla asked him to lead a new visual identity team. When Firefox 0.8 came out in February 2004, it got new branding, including new icons by silverorange, a group of web developers who had worked with Mozilla for a long time. The final pictures were made by Jon Hicks, who had worked on Camino. Later, the logo was changed to fix problems that showed when it was made larger.

The animal in the logo is a stylized fox. The name "firefox" is usually a common name for the red panda, but Hicks said the panda "didn't really conjure up the right imagery" and was not widely known.

In 2017, Mozilla made a sleeker, newer logo as part of the quantum update. In June 2019, Mozilla unveiled a revised logo, which was used starting with version 70. This was part of an effort to build a brand around Firefox and its related apps and services, which are now promoted together as a suite.

In March 2026, Mozilla named the fox mascot Kit. Kit now mostly appears apart from the globe, in Firefox's branding and in the product itself, such as error screens and settings pages. Kit was designed to feel "like your companion for this internet era," which mostly refers to the growing amount of AI content online. Along with Kit, Firefox got a new brand identity, with a new font and colors similar to the globe in the logo.

Trademark

See also: Debian–Mozilla trademark dispute

The name "Mozilla Firefox" is a registered trademark of Mozilla. The name and the official Firefox logo can only be used under certain rules. Anyone may share the official versions without changes and call them Firefox. There are limits on versions that change the underlying code. The name "Firefox" comes from a nickname of the red panda, which Mozilla celebrated. Mozilla placed the logo files under open-source licenses, but its trademark rules do not allow changed or similar logos where trademark law applies.

Some people disagreed with Mozilla's decision to stop certain open-source versions from using the "Firefox" name. In 2007, Mozilla Foundation Chairperson Mitchell Baker explained that versions could use the name if they did not change the source code. The Firefox build system has a "branding switch" that lets the code be built without the official logo and name. In 2006, the Debian project stopped using the official logo because of Debian's guidelines. Mozilla said this was not acceptable, so Debian renamed its version Iceweasel. It switched back to the Firefox name in 2016. GNU IceCat, shared by the GNU Project, is another changed version that keeps its own branding.

Firefox became popular quickly, with 100 million downloads in its first year. Starting in 2004, a series of marketing events, called "marketing weeks," was organized by Blake Ross and Asa Dotzler. On September 12, 2004, Firefox launched a marketing website called "Spread Firefox" (SFX), where people could share marketing ideas. In a campaign to break the world download record with Firefox 3, there were over eight million downloads, which earned an official Guinness world record. In February 2011, Mozilla announced that it would retire Spread Firefox, and it closed in May 2011. In 2006, the "World Firefox Day" campaign was held to celebrate the third anniversary of the founding of the Mozilla Foundation.

Firefox fans have also helped promote the browser. In 2006, some contributors from Oregon State University made a crop circle of the Firefox logo in an oat field near Amity, Oregon. When Firefox reached 500 million downloads in 2008, the community celebrated by visiting Freerice to earn 500 million grains of rice. Mozilla also ran a service called Live Chat, launched in 2007, where volunteers offered technical help. It was later retired. To promote Firefox Quantum in 2017, Mozilla worked with Reggie Watts on TV ads and social media posts. In July 2026, it was announced that Firefox would sponsor the front of the shirt of the Welsh football club Wrexham AFC for several years.

Performance

Many tests have compared how fast Firefox runs and how much computer memory it uses. In December 2005, Internet Week reported that many readers saw high memory use in Firefox 1.5. Mozilla developers said this was partly due to a new feature called FastBack, which helps pages load when you go backwards and forwards. Some add-ons, such as Google Toolbar and older versions of AdBlock, and some older plug-ins also caused problems. A 2006 test by PC Magazine found that Firefox 2 used about as much memory as Opera 9 and Internet Explorer 7. In 2006, Softpedia noted that Firefox 1.5 took longer to start up than other browsers, and more speed tests confirmed this. Internet Explorer 6 started faster on Windows XP because many of its parts were built into the system. To help, a preloader program was made to load parts of Firefox when the computer starts. A Windows Vista feature called SuperFetch does a similar job for Firefox when it is used often.

Later tests gave mixed but mostly positive results. Tests by PC World and Zimbra in 2006 found that Firefox 2 used less memory than Internet Explorer 7. Mozilla's own tests found that Firefox 3 did too. In 2009, BetaNews said Firefox 3.5 performed "nearly ten times better on XP than Microsoft Internet Explorer 7." In 2012, Tom's Hardware tested Firefox 10 against other browsers, including Internet Explorer 9, on Windows 7. It found Firefox was the best choice for that system, though it only narrowly beat Google Chrome. Tests in 2013 and 2014 also gave Firefox high marks, especially for using little memory when many tabs were open. In 2015, Firefox scored highest on some tests and lower on others. Its results on JavaScript tests were mixed. Firefox's Quantum project arrived with Firefox 57 in November 2017. It made Firefox faster than Chrome in some independent JavaScript tests. TechRadar named it the fastest web browser in a May 2019 report. In 2023, Microsoft said it had fixed a problem in Windows that had slowed down programs, especially Firefox. As of September 2025, Firefox's market share was 4.45%.

Further information: Usage share of web browsers

Firefox has been downloaded more and more since version 1.0 came out. By 31 July 2009, it had been downloaded over one billion times. These numbers do not count updates or downloads from other websites. They also do not show how many people use Firefox, since one person might download it several times or install it on many computers. In July 2010, IBM asked all of its roughly 400,000 employees to use Firefox as their default browser. Firefox was the second-most used web browser until November 2011, when Google Chrome passed it. Mozilla said that Firefox had more than 450 million users as of October 2012. In June 2026, Firefox was the fourth-most popular desktop browser, with 3.21% of worldwide usage share of web browsers across all platforms.

Mozilla's Firefox Public Data report shows that the number of desktop users each month fell from about 310 million in 2017 to 200 million in 2023. Since October 2020, Firefox has become less popular in countries where it used to be the most popular, such as Eritrea and Cuba. The governments of the UK and US both follow a "2% rule." This means that only browsers with more than 2% of visitors to their websites will be supported. Some people worry that support for Firefox could be dropped. As of 29 December 2023, it had 2.2% of visitors to US government websites.

Reception

Web developers have criticized Firefox for being slow to adopt web standards and for not fixing bugs that are decades old. They also say it lacks support for some newer features, such as view transitions, gradients, and some CSS features. Firefox scores lower than rival browsers on both HTML5test and JetStream2.

In 2025, Mozilla introduced terms of use for Firefox to explain users' rights and permissions for the browser. People criticized one part that gave Mozilla wide permission to use information sent to it while people used the browser. Some worried this could harm privacy and that Mozilla wanted to use user data to train AI models. Mozilla denied this and said the change does not give it ownership of user data. A few days later, Mozilla changed the wording of its privacy FAQ and removed a promise never to "sell your personal data."