Getting started with web-ext

web-ext is a command line tool designed to speed up various parts of the extension development process, making development faster and easier. This article explains how to install and use web-ext.


web-ext is a node-based application. You install it with brew or the nodejs npm tool.

Install with brew using:

brew install web-ext

Install with npm using:

npm install --global web-ext

web-ext requires the current LTS (long-term support) versions of NodeJS.

To test whether the installation worked run the following command, which displays the web-ext version number:

web-ext --version

web-ext will notify you when it is time to update to the newest version. To update your global install, use the command npm install -g web-ext.

Using web-ext

Before you start using web-ext locate an example extension to use—if you don’t have one, use one from the webextensions-examples repo. If you would like to start from scratch, use our community developed boilerplating tool to get started with a fresh extension.

Testing out an extension

Test an extension in Firefox by cd'ing into your extensions’s root directory and entering:

web-ext run

This starts Firefox and loads the extension temporarily in the browser, just as you can on the about:debugging page. Note that this web-ext method has the same limitations regarding prompts for permissions and restart features as about:debugging.

See the run reference guide to learn more.

Automatic extension reloading

The run command watches your source files and tells Firefox to reload the extension after you edit and save a file. For example, if you changed the name property in your manifest.json file, Firefox displays the new name. This makes it easy to try out new features because you can see the effect immediately. The automatic reloading feature is active by default, you use it like this:

web-ext run

You can also press the r key in the web-ext terminal to trigger an extension reload.

If you experience unexpected behavior with the reloading feature, please file a bug. You can also disable reloading like this:

web-ext run --no-reload

Extension reloading is only supported in Firefox 49 or higher.

Testing in different versions of Firefox

To run your extension in a version of Firefox Desktop other than the default, use the --firefox option to specify a full path to the binary file. Here is an example for Mac OS:

web-ext run --firefox=/Applications/

On Windows, the path needs to include firefox.exe, for example:

web-ext run --firefox="C:\Program Files\Mozilla Firefox\firefox.exe"

See the run command reference to learn more.

Testing in Firefox 48

Firefox 48 was the first stable version to use the WebExtension platform, but it doesn't allow web-ext to install an extension remotely. You need to run your extension in Firefox 48 using:

web-ext run --pre-install

Testing in Firefox for Android

To run your extension in Firefox for Android, follow these instructions to set up your computer and device.

With your device connected to your development computer, run:

web-ext run --target=firefox-android

This command displays the device ID for your connected Android device or devices. If you don't see a list of device IDs, make sure you set up the device for development correctly.

Now, add the device ID to the command:

web-ext run --target=firefox-android --android-device=<device ID>

If you've multiple versions of Firefox installed, you may need to choose a specific version. For example:

web-ext run --target=firefox-android ... --firefox-apk=org.mozilla.firefox

The first time you run this command, you may need to grant Android permissions for the APK. This is because the command needs read/write access to the device storage, so that Firefox for Android can run on a temporary profile. The web-ext output guides you in how to grant these permissions.

The web-ext command does not alter any of your existing Firefox for Android preferences or data. To see more information about how web-ext is interacting with your device, run the command with --verbose.

See the run command reference to learn more.

Debugging in Firefox for Android

When using web-ext run to test an extension on Firefox for Android, you'll notice a message like this in the console output:

You can connect to this Android device on TCP port 51499

This is a remote debugger port that you can connect to with Firefox's developer tools. In this case, you'd connect to host localhost on port 51499.

See this guide for more information about debugging an extension on Firefox for Android.

Testing unsigned extensions

When you execute web-ext run, the extension gets installed temporarily until you close Firefox. This does not violate any signing restrictions. If instead you create a zip file with web-ext build and try to install it into Firefox, you will see an error telling you that the add-on is not signed. You will need to use an unbranded build or use a development build to install unsigned extensions.

Using a custom profile

By default, the run command will create a temporary Firefox profile. To run your extension with a specific profile use the --firefox-profile option, like this:

web-ext run --firefox-profile=your-custom-profile

This option accepts a string containing the name of your profile or an absolute path to the profile directory. This is helpful if you want to manually configure some settings that will always be available to the run command.

Keeping profile changes

The run command does not save any changes made to the custom profile specified by --firefox-profile. To keep changes, add this option:

web-ext run --keep-profile-changes --firefox-profile=your-custom-profile

This may be helpful if your extension has many different run states.

This option makes the profile specified by --firefox-profile completely insecure for daily use. It turns off auto-updates and allows silent remote connections, among other things. Specifically, it will make destructive changes to the profile that are required for web-ext to operate.

Packaging your extension

Once you've tested your extension and verified that it's working, you can turn it into a package for submitting to using the following command:

web-ext build

This outputs a full path to the generated .zip file that can be loaded into a browser.

The generated .zip file doesn't work on Firefox without signing or adding key into manifest.json. For more information, please refer to the WebExtensions and the Add-on ID page.

web-ext build is designed to ignore files that are commonly not wanted in packages, such as .git, node_modules, and other artifacts.

See the build reference guide to learn more.

Signing your extension for self-distribution

As an alternative to publishing your extension on, you can self-host your package file but it needs to be signed by Mozilla first. The following command packages and signs a ZIP file, then returns it as a signed XPI file for distribution:

web-ext sign --api-key=$AMO_JWT_ISSUER --api-secret=$AMO_JWT_SECRET

The API options are required to specify your credentials.

  • --api-key: the API key (JWT issuer) from needed to sign the extension. This is a string that will look something like user:12345:67.
  • --api-secret: the API secret (JWT secret) from needed to sign the extension. This is a string that will look something like 634f34bee43611d2f3c0fd8c06220ac780cff681a578092001183ab62c04e009.

See the sign reference guide to learn more.

Signing extensions without an explicit ID

web-ext supports signing extensions that do not declare the property in their manifest. The first time you sign an extension without an explicit ID, will generate an ID and web-ext will save it to .web-extension-id in the working directory. You should save the ID file so that you can sign future versions of the same extension. If you lose the ID file, you will have to add back the property or use the --id option when signing, for example:

web-ext sign --api-key=... --api-secret=... --id="{c23c69a7-f889-447c-9d6b-7694be8035bc}"

Signing in a restricted environment

If you're working in an environment that restricts access to certain domains, you can try using a proxy when signing:

web-ext sign --api-key=... --api-secret=... --api-proxy=https://yourproxy:6000

See the --api-proxy option to learn more.

The following domains are used for signing and downloading files:


Signing a test version of a listed extension

If you've listed an extension on, use web-ext to create a signed but unlisted version for testing purposes. For example, you may wish to distribute an alpha or beta version to users for early feedback and testing.

First, change the version number in your manifest.json so that it is different from the latest listed version. Then, create the unlisted version by using the --channel option like this:

web-ext sign --channel=unlisted --api-key=... --api-secret=...

This signs and downloads an XPI file that can be installed into Firefox.

Once you've finished testing, to publish the extension you must define --channel as listed, as the channel option defaults to the one used previously. So, after incrementing the version in your manifest.json, run:

web-ext sign --channel=listed --api-key=... --api-secret=...

This publishes and submits your extension for review as if you had uploaded it to

Setting --channel=listed for a new version of a listed extension is not well supported. It uploads your new version to as if you'd submitted it manually. However, the command will fail and you'll have to check for the correct status.

See the sign reference guide to learn more.

Checking for code "lint"

Before trying out your extension with the run command or submitting your package to, use the lint command to make sure your manifest and other source files do not contain any errors. You can also set strict_min_version in your extension’s manifest file and lint will report on the permissions, manifest keys, and web extension APIs used that are not available in that version. Example:

web-ext lint

This uses the addons-linter library to walk through your source code directory and report any errors, such as the declaration of an unknown permission.

See the lint reference guide to learn more.

Setting option defaults in a configuration file

You can specify --config=my-config.js to set default values for any option. Here is an example with the build command:

web-ext --config=my-config.js build

The file should be a CommonJS module as understood by NodeJS and must export each configuration value. Here is how you would set the default value of --verbose to true:

module.exports = {
  verbose: true,

If you want to specify options that only apply to a specific command, you nest the configuration under the command name. Here is an example of adding configuration for --overwrite-dest that only applies to the build command as well as --firefox that only applies to the run command:

module.exports = {
  // Global options:
  verbose: true,
  // Command options:
  build: {
    overwriteDest: true,
  run: {
    firefox: 'nightly',

To create a configuration key for a command line option, you remove the preceding dashes and convert the name to camel case. As you can see from this example, --overwrite-dest was converted to overwriteDest.

If an option can be specified multiple times on the command line then you define it as an array. For example, here is how to specify multiple --ignore-files patterns:

module.exports = {
  ignoreFiles: [

web-ext will also try to load its configuration options from a "webExt" property included in the package.json file in the current directory:

  "name": "an-extension-src-dir-with-a-package-json",
  "version": "1.0.0",
  "webExt": {
    "sourceDir": "dist/extension/"

Automatic discovery of configuration files

web-ext will load existing configuration files in the following order:

  • A config file named .web-ext-config.js in your home directory, for example: - On Windows: C:\Users\<username>\.web-ext-config.js - On macOS: /Users/<username>/.web-ext-config.js - On Linux: /home/<username>/.web-ext-config.js
  • A config property named "webExt" included in a package.json file in the current directory.
  • A config file named web-ext-config.js in the current directory.

If a home directory config and a local directory config define the same option, the value from the latter file will be used.

To disable automatic loading of configuration files, set this option:

web-ext --no-config-discovery run

To diagnose an issue related to config files, re-run your command with --verbose. This will tell you which config file affected which option value.

Specifying different source and destination directories

The preceding commands use default directories for the extension source and artifact creation (for example, built .zip files). The defaults are:

  • Source: The directory you are in.
  • Artifacts: A directory called ./web-ext-artifacts, created inside the current directory.

You can specify different source and destination directories using the --source-dir and --artifacts-dir options when running your commands. Their values can be relative or absolute paths, but must always be specified as strings. Here is an example of specifying both options when building an extension:

web-ext build --source-dir=webextension-examples/notify-link-clicks-i18n --artifacts-dir=zips

Outputting verbose messages

To see in detail what web-ext is doing when you run a command, include the --verbose option. For example:

web-ext build --verbose

Viewing all commands and options

You can list all commands and options like this:

web-ext --help

You can list options for a specific command by adding it as an argument:

web-ext --help run

Detecting temporary installation

Your extension can detect whether it was installed using web-ext run, rather than as a built and signed extension downloaded from Listen for the runtime.onInstalled event and check the value of details.temporary.

Using web-ext from a script

You can use web-ext as a NodeJS module. Here is more information, with example code.