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Build and package the same extension for multiple browsers with predictable outputs. Ship the same extension to Chrome, Edge, and Firefox without maintaining separate build scripts. Extension.js runs production builds per target and writes artifacts to dist/<browser>. It can also generate zip packages for distribution.

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How it works

Run a production build: 
npx extension build
The default browser target is chromium unless you override it.

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Browser selection

You can target a specific browser/engine: 
npx extension build --browser=chrome

npx extension build --browser=firefox
Supported values include:
  • chrome
  • edge
  • firefox
  • chromium
  • chromium-based
  • gecko-based / firefox-based (aliases)
You can also run a build matrix in one command: 
npx extension build --browser=chrome,edge,firefox
This builds sequentially for chrome, edge, and firefox.

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Output layout

Each target writes to its own folder:
  • dist/chrome
  • dist/edge
  • dist/firefox
  • dist/chromium
  • dist/chromium-based
  • dist/gecko-based

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Build capabilities

OptionWhat it does
--browser=<target>Builds for a specific browser or engine family.
--zipCreates a distribution zip per target output.
--zip-filename=<name>Overrides the default zip file name.
--zip-sourceCreates a source archive alongside output.
--polyfillEnables compatibility behavior for browser.* API usage in Chromium-family targets.

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Generating a zip file

Generate a distribution zip from each target output with --zip: 
npx extension build --zip
By default, the zip name uses sanitized manifest name + version, for example:
  • my-extension-1.0.0.zip
Customize filename: 
npx extension build --zip --zip-filename=my-release
This creates my-release.zip inside the target dist/<browser> folder.

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Include source archive

Use --zip-source to generate a source archive alongside distribution output. --zip-source produces:
  • dist/<name>-<version>-source.zip

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Polyfilling browser APIs

If your code relies on Gecko-style browser.* APIs and you need Chromium compatibility, enable --polyfill: 
npx extension build --polyfill

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Best practices

  • Build per target in continuous integration (CI): Treat each browser output as an independent artifact.
  • Use a browser matrix command for parity checks: Catch target-specific issues early in one pipeline step.
  • Package intentionally: Use --zip for store uploads and --zip-source for traceable source artifacts.
  • Keep target configuration explicit: Use extension.config.* command/browser defaults for reproducible builds.

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Next steps