userScripts

Use this API to register user scripts, third-party scripts designed to manipulate webpages or provide new features. Registering a user script instructs the browser to attach the script to pages that match the URL patterns specified during registration.

This API offers similar capabilities to contentScripts but with features suited to handling third-party scripts:

  • execution is in an isolated sandbox: each user script is run in an isolated sandbox within the web content processes, preventing accidental or deliberate interference among scripts.
  • access to the window and document global values related to the webpage the user script is attached to.
  • no access to WebExtension APIs or associated permissions granted to the extension: the API script, which inherits the extension’s permissions, can provide packaged WebExtension APIs to registered user scripts. An API script is declared in the extension's manifest file using the "user_scripts" manifest key.

This API requires the presence of the user_scripts key in the manifest.json, even if no API script is specified. For example. user_scripts: {}.

To use the API, call register() passing in an object defining the scripts to register. The method returns a Promise that is resolved with a RegisteredUserScript object.

User scripts are unregistered when the related extension page (from which the user scripts were registered) is unloaded, so you should register a user script from an extension page that persists at least as long as you want the user scripts to stay registered.

Types

userScripts.RegisteredUserScript
The object returned by the register() method. It represents the registered user scripts and is used to deregister the user scripts.

Methods

userScripts.register()
Registers user scripts.

Events

userScripts.onBeforeScript
An event available to the API script, registered in"user_scripts", that execute before a user script executes. Use it to trigger the export of the additional APIs provided by the API script, so they are available to the user script.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxOperaSafariFirefox for Android
RegisteredUserScriptChrome No support NoEdge No support NoFirefox Full support 68
Full support 68
Full support 66
Disabled
Disabled From version 66: this feature is behind the extensions.webextensions.userScripts.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera No support NoSafari No support NoFirefox Android Full support 68
RegisteredUserScript.unregisterChrome No support NoEdge No support NoFirefox Full support 68
Full support 68
Full support 66
Disabled
Disabled From version 66: this feature is behind the extensions.webextensions.userScripts.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera No support NoSafari No support NoFirefox Android Full support 68
onBeforeScriptChrome No support NoEdge No support NoFirefox Full support 68
Full support 68
Full support 66
Disabled
Disabled From version 66: this feature is behind the extensions.webextensions.userScripts.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera No support NoSafari No support NoFirefox Android Full support 68
registerChrome No support NoEdge No support NoFirefox Full support 68
Full support 68
Full support 66
Disabled
Disabled From version 66: this feature is behind the extensions.webextensions.userScripts.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera No support NoSafari No support NoFirefox Android Full support 68

Legend

Full support  
Full support
No support  
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

See also