Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation. It uses the Gecko rendering engine to display HyperText Markup Language (HTML) pages, Cascading Style Sheets (CSS) and JavaScript code. It runs on Windows, macOS, Linux, Android and iOS.
History of Firefox
Creator: Dave Hyatt, Joe Hewitt and Blake Ross, within the Mozilla community. Year: 2002.
Firefox is a web browser. It was created in 2002 under the codename Phoenix. Dave Hyatt, Joe Hewitt and Blake Ross began it. It started as an experimental branch of the Mozilla project. They judged that the Mozilla Suite was bloated. So they built a standalone browser to replace it. Phoenix was renamed in 20031. A trademark claim caused it.
Netscape created the Mozilla community in 1998. The browser is the spiritual successor of Netscape Navigator. In the beta phase, testers praised its speed, security and add-ons. They compared it with Microsoft Internet Explorer 6. It then dominated the market.
Firefox 1.0 was released on November 9, 2004. It ran on Windows 95 and later Windows versions. It reached 60 million downloads in nine months. By July 31, 2009, it had more than one billion downloads. These figures count downloads. They do not count active users.
Its usage share peaked in November 2009. It was 32.21%. That month, Firefox 3.5 passed Internet Explorer 7. Its share later fell as Google Chrome grew. In November 2017, it added the Quantum project. It made the browser faster. It did this with parallel processing.
The mobile version was code-named Fennec. It was first released for Maemo in January 2010. It came to Android in March 2011. On September 1, 2026, Smart Window became available. It is an AI assistant. It came in Firefox 155.0. It is for users in the USA, Canada and France. AI stands for artificial intelligence.
Changelog and latest update
Firefox 4 was the first release with HTML5 and CSS3 support. It has passed the Acid2 standards test since version 3.0. Acid2 is a test page. It checks how a browser draws web standards. Firefox 4 and later also scored 100 out of 100 on the Acid3 test. This happened after its SVG font section was removed in 2011.
Firefox 57 came out in November 2017. It moved the browser to a multi-process model. Older add-ons used the XUL and XPCOM interfaces. Those add-ons stopped working. Add-ons now use WebExtensions. They are written with HTML, CSS and JavaScript. They were designed to match the extension systems of Chrome and Microsoft Edge.
Support ended on some older systems. It no longer runs on Windows 8.1 and below. It no longer runs on macOS 10.14 and below. The official download page sends those users to Firefox ESR. ESR means Extended Support Release. ESR gets security updates for a longer time.
It was discontinued on Amazon Fire TV on April 30, 2021. Wikipedia says it remains the default browser on Debian and Ubuntu. Wikipedia says Smart Window appeared in Firefox 155.0 in September 2026. Smart Window is an AI assistant. It works inside the browser. Wikipedia cites news coverage for this.
Latest update: Firefox 157.0, 2026-09-29
Version 157.0 reached Release channel users on September 29, 2026. Mozilla says it is the largest visual refresh of the browser in years. It adds built-in light and dark themes. It adds a compact mode with less toolbar spacing. It adds hardware AV1 decoding for WebRTC video calls.
Usage examples
Websites do not call Firefox directly. A site works in Firefox when it follows the standard HTML, CSS and JavaScript rules. Users and developers control the browser with preferences, extension files and command line options. The examples below show three common patterns. Each note states the purpose of its example. A reader can then judge when to use it.
user_pref("network.http.http3.enable",
true);
user_pref(
"dom.security.https_only_mode",
true);This file sits in a Firefox profile folder. It sets two preferences when the browser starts. The first turns on HTTP/3, a newer web transport protocol. The second forces HTTPS, the encrypted form of HTTP, for every site.
{
"manifest_version": 3,
"name": "Page Notes",
"version": "1.0",
"browser_specific_settings": {
"gecko": {
"id": "notes@example.com"
}
}
}A WebExtension needs this manifest file to load in Firefox. The manifest_version 3 format is the current standard. Firefox uses the gecko id to identify the add-on. The gecko id is a unique address. It is read when the add-on is installed.
firefox --headless \
--screenshot shot.png \
https://example.comThis command starts Firefox without a window. It loads the page. It saves a picture of it as shot.png. Developers use it to check a page layout. You can change the file name and the page address to any values.
References
These sources are outside Websnoogie and were checked on 2026-10-12.
Firefox
Wikipedia
Encyclopedia entry on the Mozilla browser. It covers the 2002 origin as Phoenix, the 2004 release, the Quantum project, the platforms, the standards support, the usage share and the Smart Window release, with a list of sources.
Firefox Release Notes
Mozilla
The official list of every Firefox version, including release channel and Extended Support Release builds. It links to the notes for each version, so readers can find the date and the changes for any release. Each release is listed with its date.
Firefox 157.0 Release Notes
Mozilla
The notes for Firefox 157.0, first offered on September 29, 2026. They list the new visual design, the built-in themes, the compact mode, the AV1 hardware decoding and the security fixes in that release.
Learn About Mozilla
Mozilla
The Mozilla page that explains the non-profit organization behind Firefox. It describes the mission, the open-source projects and the governance of the Mozilla Foundation and its subsidiary, the Mozilla Corporation.
Firefox: The Fast, Private Browser
Mozilla
The official Firefox download page. It lists the operating systems that receive the current release and the systems that must use Firefox ESR, plus the privacy features built into the browser.
A page should work in Firefox too
Our build takes 3 to 5 days, and Firefox is one of the browsers we open each page in before launch. Firefox is a web browser, the program people use to open a website. Every browser draws a page in its own way. A menu that looks right in one browser can shift in another, so we test each page in Firefox directly.
Testing means more than a quick glance. We check the menu, the forms and the photos. We look for text that runs off the edge of the screen. We also read the page title, because Firefox shows that title in its tab. A small fix before launch saves a visitor from a broken page later.
The new-site package is $300, paid once, and it covers a handful of pages: up to five plus one contact page. Local SEO is $190 a month for continued care after launch. Both options keep your pages readable and current. You choose the one that fits your budget and your timeline.
Paste your current site address into a message, and we will open it in Firefox and report back. For a quick look by phone, call 402-813-4034.
