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Use install to add a managed browser runtime into the Extension.js cache. This is most useful when you want a consistent browser binary for dev, build, start, or preview. It supports Chrome for Testing, Chromium, Firefox, and Edge.

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When to use install

  • You need a consistent, repeatable browser binary for continuous integration (CI), automation, or team-consistent local runs.
  • You want Chrome for Testing instead of relying on whatever Chrome version your system has installed.
  • You are setting up cross-browser testing with managed Firefox or Edge runtimes.

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Canonical usage

For a single browser, use the positional form: 
extension install <browser>
Use --browser only when you need multiple targets, browser families, or all.

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Install command capabilities

CapabilityWhat it gives you
Managed browser cacheStable install location under the Extension.js browser cache
Repeatable runtimeConsistent binaries for repeatable local runs and automation
Cross-browser setupOne command flow for Chrome, Chromium, Edge, and Firefox
Path discovery--where reveals the resolved cache root or browser-specific install path

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Usage

extension install [browser-name] [options]

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Arguments and flags

Flag / argumentWhat it doesDefault
[browser-name]Install a single browser target such as chrome, chromium, edge, or firefoxchromium
--browser <chrome|chromium|edge|firefox|chromium-based|gecko-based|firefox-based|all>Override the positional browser name and support multi-target installsunset
--wherePrint the resolved managed cache root, or browser-specific install pathdisabled

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Examples

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Install Chrome for Testing

extension install chrome

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Install multiple targets in one command

extension install --browser chrome,firefox

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Show the managed install path for Chrome

extension install chrome --where

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Cache locations

By default, Extension.js stores managed browsers in a stable per-user cache:
  • macOS: ~/Library/Caches/extension.js/browsers
  • Linux: ~/.cache/extension.js/browsers or $XDG_CACHE_HOME/extension.js/browsers
  • Windows: %LOCALAPPDATA%\extension.js\browsers
You can override the cache root with EXT_BROWSERS_CACHE_DIR.

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Best practices

  • Use install in CI to pin a consistent browser binary instead of relying on whatever the runner provides.
  • Prefer chrome over chromium for Chrome for Testing — it matches stable Chrome behavior more closely.
  • Use --where to verify cache paths before scripting automation around managed browsers.
  • install only manages browsers inside the Extension.js cache. It does not modify system browser installs.

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Behavior notes

  • chrome installs Chrome for Testing rather than relying on the system Google Chrome app.
  • edge may require a privileged interactive session on Linux.

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Next steps