Note: User Scripts are automatically 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.
const registeredUserScript = await browser.userScripts.register( userScriptOptions // object ); … await registeredUserScript.unregister()
Promise that is resolved once the user scripts are unregistered. The promise does not return a value.
BCD tables only load in the browser