Marionette is a remote-control for Firefox and other Mozilla products. It is similar to Selenium.
Marionette is an automation driver for Mozilla's Gecko engine. It can remotely control either the UI or the internal JavaScript of a Gecko platform, such as Firefox or Firefox OS. It can control both the chrome (i.e. menus and functions) or the content (the webpage loaded inside the browsing context), giving a high level of control and ability to replicate user actions. In addition to performing actions on the browser, Marionette can also read the properties and attributes of the DOM.