Storybook for Firefox

Storybook is an interactive tool that creates a playground for UI components. We use Storybook to document our design system, reusable components, and any specific components you might want to test with dummy data. Take a look at our Storybook instance!


Storybook lists components that can be reused, and helps document what common elements we have. It can also list implementation specific components, but they should be added to the “Domain-Specific UI Widgets” section.

Changes to files directly referenced from Storybook (so basically non-chrome:// paths) should automatically reflect changes in the opened browser. If you make a change to a chrome:// referenced file then you’ll need to do a hard refresh (Cmd+Shift+R/Ctrl+Shift+R) to notice the changes. If you’re on Windows you may need to ./mach build faster to have the chrome:// URL show the latest version.

Running Storybook

Installing the npm dependencies and running the storybook npm script should be enough to get Storybook running. This can be done via ./mach storybook commands, or with your personal npm/node that happens to be compatible.

Running with mach commands

This is the recommended approach for installing dependencies and running Storybook locally.

To install dependencies, start the Storybook server, and launch the Storybook site in a local build of Firefox, just run:

# This uses npm ci under the hood to install the package-lock.json exactly.
./mach storybook

This single command will first install any missing dependencies then start the local Storybook server. It will also start your local browser and point it to http://localhost:5703 while enabling certain preferences to ensure components display as expected (specifically svg.context-properties.content.enabled and layout.css.light-dark.enabled).

It’s necessary to use your local build to test in Storybook since chrome:// URLs are currently being pulled from the running browser, so any changes to common-shared.css for example will come from your build.

The Storybook server will continue running and will watch for component file changes.

Alternative mach commands

Although running ./mach storybook is the most convenient way to interact with Storybook locally it is also possible to run separate commands to start the Storybook server and run your local build with the necessary prefs.

If you only want to start the Storybook server - for example in cases where you already have a local build running - you can pass a --no-open flag to ./mach storybook:

# Start the storybook server without launching a local Firefox build.
./mach storybook --no-open

If you just want to spin up a local build of Firefox with the required prefs enabled you can use the launch subcommand:

# In another terminal:
./mach storybook launch

This will run your local browser and point it at http://localhost:5703.

Alternatively, you can simply navigate to http://localhost:5703/ or run:

# In another terminal:
./mach run http://localhost:5703/

although with this option certain prefs won’t be enabled, so what’s displayed in Storybook may not exactly reflect how components will look when used in Firefox.

Personal npm

You can use your own npm to install and run Storybook. Compatibility is up to you to sort out.

cd browser/components/storybook
npm ci # Install the package-lock.json exactly so lockfileVersion won't change.
npm run storybook

Updating Storybook dependencies

On occasion you may need to update or add a npm dependency for Storybook. This can be done using the version of npm packaged with mach:

# Install a dev dependency from within the storybook directory.
cd browser/components/storybook && ../../../mach npm i -D your-package

Adding new stories

Storybook is currently configured to search for story files (any file with a .stories.(js|mjs|md) extension) in toolkit/content/widgets and browser/components/storybook/stories.

Stories in toolkit/content/widgets are used to document design system components, also known as UI widgets. As long as you used ./mach addwidget correctly, there is no additional setup needed to view your newly created story in Storybook.

Stories in browser/components/storybook/stories are used for non-design system components, also called domain-specific UI widgets. The easiest way to use Storybook for non-design system element is to use ./mach addstory new-component "Your Project". You can also use ./mach addstory new-component "Your Project" --path browser/components/new-component.mjs where --path is the path to your new components’ source. See the Credential Management/Timeline widget for an example.

If you want to colocate your story with the code it is documenting you will need to add to the stories array in the .storybook/main.js configuration file so that Storybook knows where to look for your files.

The Storybook docs site has a good overview of what’s involved in writing a new story. For convenience you can use the Lit library to define the template code for your story, but this is not a requirement.

UI Widgets versus Domain-Specific UI Widgets

Widgets that are part of our design system and intended to be used across the Mozilla suite of products live under the “UI Widgets” category in Storybook and under toolkit/content/widgets/ in Firefox. These global widgets are denoted in code by the moz- prefix in their name. For example, the name moz-support-link informs us that this widget is design system compliant and can be used anywhere in Firefox.

Storybook can also be used to help document and prototype widgets that are specific to a part of the codebase and not intended for more global use. Stories for these types of widgets live under the “Domain-Specific UI Widgets” category, while the code can live in any appropriate folder in mozilla-central. See the Credential Management folder as an example of a domain specific folder and see the login-timeline.stories.mjs for how to make a domain specific folder in Storybook. To add a non-team specific widget to the “Domain-specific UI Widgets” section, see the migration-wizard.stories.mjs file.

Creating and documenting domain specific UI widgets allows other teams to be aware of and take inspiration from existing UI patterns. With these widgets, there is no guarantee that the element will work for your domain. If you need to use a domain-specific widget outside of its intended domain, it may be worth discussing how to convert this domain specific widget into a global UI widget.