Firefox Home (New Tab)

All files related to Firefox Home, which includes content that appears on about:home, about:newtab, and about:welcome, can we found in the browser/components/newtab directory. Some of these source files (such as .js, .jsx, and .sass) require an additional build step. We are working on migrating this to work with mach, but in the meantime, please follow the following steps if you need to make changes in this directory:

For .jsm files

No build step is necessary. Use mach and run mochi tests according to your regular Firefox workflow.

For .js, .jsx, .sass, or .css files


You will need the following:

  • Node.js 8+ (On Mac, the best way to install Node.js is to use the [install link on the Node.js homepage](
  • npm (packaged with Node.js)

To install dependencies, run the following from the root of the mozilla-central repository (or cd into browser/components/newtab to omit the –prefix in any of these commands):

npm install --prefix browser/components/newtab

Which files should you edit?

You should not make changes to .js or .css files in browser/components/newtab/css or browser/components/newtab/data directory. Instead, you should edit the .jsx, .js, and .sass files in browser/components/newtab/content-src directory.

Building assets and running Firefox

To build assets and run Firefox, run the following from the root of the mozilla-central repository:

npm run bundle --prefix browser/components/newtab && ./mach run

Running tests

Mochi tests and xpcshell tests can be run normally. To run our additional unit tests, you can run the following:

npm test --prefix browser/components/newtab

The Newtab team is currently responsible for fixing any test failures that result from changes until these tests are running in Try, so this is currently an optional step.

GitHub workflow

The files in this directory, including vendor dependencies, are synchronized with the repository. If you prefer a GitHub-based workflow, you can look at the documentation there to learn more.