Firefox is Mozilla's popular Web browser, available for multiple platforms including Windows, macOS, and Linux on the desktop and all Android and iOS mobile devices. With broad compatibility, the latest in Web technologies, and powerful development tools, Firefox is a great choice for both Web developers and end users.

Firefox is an open source project; much of the code is contributed by our huge community of volunteers. Here you can learn about how to contribute to the Firefox project and you will also find links to information about the construction of Firefox add-ons, using the developer tools in Firefox, and other topics.

Learn how to create add-ons for Firefox, how to develop and build Firefox itself, and how the internals of Firefox and its subprojects work.

  • Developer release notes

    Developer-focused release notes; learn what new capabilities for both Web sites and add-ons arrive in each version of Firefox.

  • Project documentation

    Get detailed information about the internals of Firefox and its build system, so you can find your way around in the code.

  • Developer guide

    Our developer guide provides details on how to get and compile the Firefox source code, how to find your way around, and how to contribute to the project.

Firefox channels

Firefox is available in five channels.

Firefox Nightly

Each night we build Firefox from the latest code in mozilla-central. These builds are for Firefox developers or those who want to try out the very latest cutting edge features while they're still under active development.

Download Firefox Nightly

Firefox Developer Edition

This is a version of Firefox tailored for developers. Every six weeks, we take the features in Firefox Nightly that are stable enough and create a new version of Firefox Developer Edition. We also add some extra features for developers that are only available in this channel.

Learn more about Firefox Developer Edition.

Download Firefox Developer Edition

Firefox Beta

After spending six weeks in Firefox Developer Edition, we take the features that are stable enough, and create a new version of Firefox Beta. Firefox Beta builds are for Firefox enthusiasts to test what's destined to become the next released Firefox version.

Download Firefox Beta


After stabilizing for another six weeks in Beta, we're ready to ship the new features to hundreds of millions of users in a new release version of Firefox.

Download Firefox

Firefox Extended Support Release (ESR)

Firefox ESR is the long-term support edition of Firefox for desktop for use by organizations including schools, universities, businesses and others who need extended support for mass deployments.

Learn more about Firefox Extended Support Release.

Download Firefox ESR


Firefox developer release notes
Нижче ви знайдете посилання на примітки до випуску розробникам для кожної нової версії Firefox. Ці з любв'ю оброблені примітки містять детальну інформацію про те, які функції додані вдосконалені і які помилки були усунені в кожній версії Firefox. Все написано, щоб дати розробникам інформацію, необхідну їм найбільше. Ласкаво просимо.
Firefox ESR
Firefox з розширеною підтримкою (Extended Support Release - ESR) заснована на офіційній версії Firefox для настільних ПК, для використання організаціями, яким потрібна розширена підтримка для масового розгортання. Unlike other release channels, ESRs are not updated with new features every six weeks.Rather,they are supported for about a year and only updated with major security or stability fixes. The current ESR version is based on Firefox 45 issued on March 8th, 2016. The next ESR version will be released on December 27th, 2016 and will be number 52.
Multiprocess Firefox
In older versions of Firefox for desktop, the entire browser ran within a single operating system process. Specifically, the JavaScript that ran the browser UI (also known as "chrome code") and the JavaScript that ran within web pages (also known as "content" or "web content") were not separated.

Currently, the latest versions of Firefox run the browser UI and the web content in separate processes. In the current iteration of this architecture, all browser tabs run within the same process and the browser UI runs in its own individual process. In future iterations of Firefox, there will be more than one process to exclusively handle web content. The internal name for this project is called Electrolysis, sometimes abbreviated to e10s.
Експериментальні функції в Firefox
In order to test new features, Mozilla publishes a test version of the Firefox browser, Firefox Nightly, every day. Experimental features, for example implementations of proposed Web platform standards, are available. This page lists features that are in Nightly versions of Firefox along with information on how to activate them, if necessary. You can test your Web sites and applications before these features get released and ensure everything will still work with the latest Web technology capabilities.

Firefox profiles

If you find yourself using multiple Firefox channels—or just multiple configurations—on a regular basis, you should read how to use multiple Firefox profiles by turning Firefox's Profile Manager and other profile management tools to your advantage.

See also