8.1.0 • Public • Published


This is a command line tool to help build, run, and test WebExtensions.

CircleCI codecov npm version

Ultimately, it aims to support browser extensions in a standard, portable, cross-platform way. Initially, it will provide a streamlined experience for developing Firefox Extensions.


Here are the commands you can run. Click on each one for detailed documentation or use --help on the command line, such as web-ext build --help.

  • run
    • Run the extension
  • lint
    • Validate the extension source
  • sign
    • Sign the extension so it can be installed in Firefox
  • build
    • Create an extension package from source
  • docs
    • Open the web-ext documentation in a browser


Using npm

First, make sure you are running the current LTS (long term support) version of NodeJS.

Global command

You can install this command onto your machine globally with:

npm install --global web-ext

For your project

Alternatively, you can install this command as one of the devDependencies of your project. This method can help you control the version of web-ext as used by your team.

npm install --save-dev web-ext

Next you can use the web-ext command in your project as an npm script. Here is an example where the --source-dir argument specifies where to find the source code for your extension.


"scripts": {
  "start:firefox": "web-ext run --source-dir ./extension-dist/",

You can always pass in additional commands to your npm scripts using the -- suffix. For example, the previous script could specify the Firefox version on the command line with this:

npm run start:firefox -- --firefox=nightly

Using Homebrew (unofficial)

The community maintains a web-ext formula.

brew install web-ext

Installation from source

You'll need:

Optionally, you may like:

  • nvm, which helps manage node versions

If you had already installed web-ext from npm, you may need to uninstall it first:

npm uninstall --global web-ext

Change into the source and install all dependencies:

git clone https://github.com/mozilla/web-ext.git
cd web-ext
npm ci

Build the command:

npm run build

Link it to your node installation:

npm link

You can now run it from any directory:

web-ext --help

To get updates, just pull changes and rebuild the executable. You don't need to relink it.

cd /path/to/web-ext
git pull
npm run build

Using web-ext in NodeJS code

Note: There is limited support for this API.

Aside from using web-ext on the command line, you may wish to execute web-ext in NodeJS code.

As of version 7.0.0, the web-ext npm package exports NodeJS native ES modules only. If you are using CommonJS, you will have to use dynamic imports.


You are able to execute command functions without any argument validation. If you want to execute web-ext run you would do so like this:

import webExt from 'web-ext';

      // These are command options derived from their CLI conterpart.
      // In this example, --source-dir is specified as sourceDir.
      firefox: '/path/to/Firefox-executable',
      sourceDir: '/path/to/your/extension/source/',
      // These are non CLI related options for each function.
      // You need to specify this one so that your NodeJS application
      // can continue running after web-ext is finished.
      shouldExitProgram: false,
  .then((extensionRunner) => {
    // The command has finished. Each command resolves its
    // promise with a different value.
    // You can do a few things like:
    // extensionRunner.reloadAllExtensions();
    // extensionRunner.exit();

If you would like to run an extension on Firefox for Android:

import * as adbUtils from "web-ext/util/adb";

// Path to adb binary (optional parameter, auto-detected if missing)
const adbBin = "/path/to/adb";
// Get an array of device ids (Array<string>)
const deviceIds = await adbUtils.listADBDevices(adbBin);
const adbDevice = ...
// Get an array of Firefox APKs (Array<string>)
const firefoxAPKs = await adbUtils.listADBFirefoxAPKs(
  deviceId, adbBin
const firefoxApk = ...

  target: 'firefox-android',
  sourceDir: ...
}).then((extensionRunner) => {...});

If you would like to control logging, you can access the logger object. Here is an example of turning on verbose logging:

import * as webExtLogger from 'web-ext/util/logger';

webExt.cmd.run({ sourceDir: './src' }, { shouldExitProgram: false });

You can also disable the use of standard input:

webExt.cmd.run({ noInput: true }, { shouldExitProgram: false });

web-ext is designed for WebExtensions but you can try disabling manifest validation to work with legacy extensions. This is not officially supported.

  { sourceDir: './src' },
    getValidatedManifest: () => ({
      name: 'some-fake-name',
      version: '1.0.0',
    shouldExitProgram: false,

Should I Use It?

Yes! The web-ext tool enables you to build and ship extensions for Firefox. This platform stabilized in Firefox 48 which was released in April of 2016.

Get Involved

Hi! This tool is under active development. To get involved you can watch the repo, file issues, create pull requests, or contact us to ask a question. Read the contributing section for how to develop new features.

Some Questions and Answers

Why do we need a command line tool?

This is a great question and one that we will ask ourselves for each new web-ext feature. Most WebExtension functionality is baked into the browsers themselves but a complimentary command line tool will still be helpful. Here is a partial list of examples:

  • File watching.
    • When you edit a file, you may need to trigger certain commands (tests, installation, etc).
  • Integrating with services.
    • Mozilla offers some useful services such as linting and signing extensions.

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npm i web-ext

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