mozilla-central

This is the main source code repository for Mozilla Firefox, the web browser. It contains all the code that makes Firefox work—from the rendering engine that displays websites, to the UI you click on, to the networking and security layers that protect your privacy.

If you've ever downloaded Firefox and wondered where all that code lives, this is it. When Mozilla engineers make changes to Firefox, they commit them here. Every new feature, bug fix, and security update flows through this repository before reaching the millions of people who use the browser.

The repository is quite large because it includes many interconnected pieces. There's code for handling different file formats, managing tabs and windows, integrating with your operating system, and much more. It's written in multiple languages depending on the component—some parts use C++, others use JavaScript or Rust, which Mozilla chose for its safety guarantees in sensitive areas.

You might explore this repository if you're a developer interested in how browsers work under the hood, want to contribute improvements to Firefox, or need to build a custom version of the browser for your organization. The README here doesn't include extensive setup or explanation, so if you're planning to dig in, you'd likely need to refer to Mozilla's developer documentation for guidance on building and testing.