Is Firefox open-source? And what does it mean

Modified Nov. 3, 2023, 8:42 p.m.


Everyone is saying that Firefox is open-source, but is it the truth? What does it really mean? I answer these questions in this article, helping you to understand.

Where to find the source code of Firefox?

Unlike a lot of other software that is using GitHub as its version control system, Mozilla is using mercurial as its source control management tool, which they are hosting on their servers.

Mercurial is less popular than git, the most popular distributed version control system, but they are both similar and have a lot of functions in common.

You can find the source code of Firefox at this URL You can also find the source code of all the open-source Mozilla projects, such as Firefox for mobile.

Is Firefox really open-source?

We have seen that the source code is available to everyone on the web, but open-source does not only mean having the source code available, it also means that the license allows everyone to reuse the source code.

The Mozilla Firefox project is developed under the Mozilla Public License, the MPL, this license is developed and maintained by Mozilla itself and is used for most of the Mozilla Foundation software.

The MPL is a completely free and open-source weak copyleft license. I won’t speak about the details here but it means that all software under this license allows free use, modification, distribution, and exploitation of the work. But it does not grant the licensee any rights to a contributor’s trademarks.

When did Firefox become open-source?

Firefox was released as an already open-sourced project in 2004. The Mozilla project was created in 1998 with his first web browser, and even this very first browser of Mozilla had been released under an open-source license, the Mozilla Project License in its 1.0 version.

So Firefox has always been open-source, even Firefox Nightly, the beta version, is open-source.

Other famous Mozilla open-source projects

The Mozilla Foundation developed a lot of other software than Firefox, and most of them are under the same open-source Mozilla Project License, here are some examples.

Mozilla Thunderbird

The second most famous Mozilla project, Thunderbird is a completely free and open-source email client, which now also has other features such as a calendar, a task manager, or an instant messaging tool.

It's running on a lot of different devices, you can even get ThunderBird on Chromebooks.

Firefox Reality

Firefox Reality is a web browser designed to be used in virtual reality, fast and secure. They are collaborating with the big companies working around virtual reality to make a better user experience in web browsing even in virtual reality. Firefox Reality is currently available in Viveport, Oculus Go, and Google Daydream.


Mozilla is also famous in the development world, they built a lot of tools, libraries, and components very useful for developers. They are, for example, the origin of the programming languages JavaScript and Rust, or the bug tracker software Bugzilla.



Maxime Levesque is a technical engineer with more than 5 years of professional experience. He is an expert in computer and phones, mostly on Apple products. Maxime is also the founder of TechBrowser.

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