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Multiple Browsers

You can build an extension for any combination of browser and manifest version. Different browsers and manifest versions support different APIs and entrypoints, so be sure to check that your extension functions as expected for each target.

Separate build targets are written to their own output directories:

└─ .output
   ├─ chrome-mv3
   ├─ firefox-mv2
   ├─ edge-mv3
   └─ ...

Target Browser

To build for a specific browser, pass the -b --browser flag from the CLI:

wxt --browser firefox
wxt build --browser firefox

By default, it will build for chrome. When excluding the manifest version flags, it will default to the commonly accepted manifest version for that browser.

BrowserDefault Manifest Version
Any other string3


To configure which browser is opened when running dev mode via wxt -b <browser>, see the web-ext.config.ts docs.

Target Manifest Version

To build for a specific manifest version, pass either the --mv2 flag or --mv3 flag from the CLI.

wxt --mv2
wxt build --mv2

When the -b --browser flag is not passed, it defaults to chrome. So here, we're targeting MV2 for Chrome.

Customizing Entrypoints

There are several ways to customize entrypoint definitions per browser.

First, you can use either the include or exclude option to include or exclude the entrypoint from specific browsers. Here are some examples

export default defineBackground({
  // Only include a background script when targeting chrome
  include: ['chrome'],
export default defineContentScript({
  // Do not add this content script to the manifest when targeting firefox
  exclude: ['firefox'],
<!-- entrypoints/options.html -->
    <!-- Don't include the options page for safari -->
    <meta name="manifest.exclude" content="['safari']" />

Second, you can change individual options per-browser:

export default defineBackground({
  persistent: {
    // Use a non-persistent background script for just safari
    safari: false,
export default defineContentScript({
  matches: {
    // Run the content script on different pages for each browser
    chrome: ['*://**'],
    firefox: ['*://**'],
    edge: ['*://**'],


Only defineBackground and defineContentScript support per-browser options right now.


To determine the browser or manifest version at runtime, you can use any of the below variables:

  • import.meta.env.BROWSER: A string, the target browser, usually equal to the --browser flag
  • import.meta.env.MANIFEST_VERSION: A number, either 2 or 3, depending on the manifest version targeted
  • import.meta.env.CHROME: A boolean equivalent to import.meta.env.BROWSER === "chrome"
  • import.meta.env.FIREFOX: A boolean equivalent to import.meta.env.BROWSER === "firefox"
  • import.meta.env.EDGE: A boolean equivalent to import.meta.env.BROWSER === "edge"
  • import.meta.env.SAFARI: A boolean equivalent to import.meta.env.BROWSER === "safari"
  • import.meta.env.OPERA: A boolean equivalent to import.meta.env.BROWSER === "opera"
  • import.meta.env.COMMAND: A string, "serve" when running wxt for development or "build" in all other cases.


These variables are constants defined at build time based on the build target. They do not actually detect which browser the code is running in.

For example, if you build for --browser chrome and publish it on Edge, import.meta.env.BROWSER will be "chrome", not "edge". You have to build a separate ZIP for --browser edge before import.meta.env.BROWSER will be "edge".

If you need to know the actual browser your code is being ran on, you should use a user agent parser.