userScripts (Legacy)

Warning:This is documentation for the legacyuserScripts API. It's available in Firefox for Manifest V2. For functionality to work with user scripts in Manifest V3 see the new userScripts API.

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 tocontentScripts 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 thewindow anddocument 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.

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

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

Note: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: Theobject returned by theregister() method. It represents the registered user scripts and is used to deregister the user scripts.
userScripts.UserScriptOptions: Theobject passed to theregister() method. It represents the content scripts to register.

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.