Firefox Welcome Experience (about:welcome)

Files related to the Firefox welcome experience, which includes content that appears on about:welcome, can be found in the browser/components/aboutwelcome directory. Some of these source files (such as .js, .jsx, and .scss) 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 `.sys.mjs` files (system modules)

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

For `.js`, `.jsx`, `.scss`, or `.css` files

Prerequisites

You will need the following:

Node.js 10+ (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. (Using mach to call npm and node commands will ensure you’re using the correct versions of Node and npm.)

(cd browser/components/aboutwelcome && ../../../mach npm install)

Which files should you edit?

You should not make changes to .js or .css files in the browser/components/aboutwelcome/content directory. Instead, you should edit the .jsx, .js, and .scss source files in browser/components/aboutwelcome/content-src directory. These files will be compiled into the .js and .css files.

Building assets and running Firefox

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

./mach npm run bundle --prefix=browser/components/aboutwelcome && ./mach build && ./mach run

Continuous development / debugging

Running ./mach npm run watchmc --prefix=browser/components/aboutwelcome will start a process that watches files in aboutwelcome and rebuilds the bundled files when JS or CSS files change.

IMPORTANT NOTE: This task will add inline source maps to help with debugging, which changes the memory footprint. Do not use the watchmc task for profiling or performance testing!

Running tests

About:welcome unit tests are written using mocha, and other errors that may show up there are SCSS issues flagged by stylelint. These things are all run using npm test under the aboutwelcome slug in Treeherder/Try, so if that slug turns red, these tests are what is failing. To execute them, do this:

./mach npm test --prefix=browser/components/aboutwelcome

Windows isn’t currently supported by npm test (path/invocation difference). To run tests that aren’t covered by mach lint and mach test:

./mach npm run lint:stylelint --prefix=browser/components/aboutwelcome
./mach npm run testmc:build --prefix=browser/components/aboutwelcome
./mach npm run testmc:unit --prefix=browser/components/aboutwelcome

Mochitests run normally, using mach test browser/components/aboutwelcome.

Code Coverage

Our testing setup will run code coverage tools in addition to just the unit tests. It will error out if the code coverage metrics don’t meet certain thresholds.

If you see any missing test coverage, you can inspect the coverage report by running

./mach npm test --prefix=browser/components/aboutwelcome &&
./mach npm run debugcoverage --prefix=browser/components/aboutwelcome