Firefox supports several remote protocols, which allow to inspect and control the browser, usually for automation purposes:
The following documentation pages apply to all remote protocols
Marionette is used both by internal tools and testing solutions, but also by geckodriver to implement the WebDriver (HTTP) specification. The documentation for Marionette can be found under testing/marionette.
Remote Protocol (CDP)¶
Firefox implements a subset of the Chrome DevTools Protocol (CDP) in order to support third party automation tools such as puppeteer. The documentation for the remote protocol (CDP) implement can be found at remote/cdp.