Introduction to Marionette

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. 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.

If this sounds similar to Selenium/WebDriver then you’re correct! Marionette shares much of the same ethos and API as Selenium/WebDriver, with additional commands to interact with Gecko’s chrome interface. Its goal is to replicate what Selenium does for web content: to enable the tester to have the ability to send commands to remotely control a user agent.

How does it work?

Marionette consists of two parts: a server which takes requests and executes them in Gecko, and a client. The client sends commands to the server and the server executes the command inside the browser.

When would I use it?

If you want to perform UI tests with browser chrome or content, Marionette is the tool you’re looking for! You can use it to control either web content, or Firefox itself.

A test engineer would typically import the Marionette client package into their test framework, import the classes and use the class functions and methods to control the browser. After controlling the browser, Marionette can be used to return information about the state of the browser which can then be used to validate that the action was performed correctly.

Using Marionette

Marionette combines a gecko component (the Marionette server) with an outside component (the Marionette client), which drives the tests. The Marionette server ships with Firefox, and to use it you will need to download a Marionette client or use the in-tree client.


Please file any bugs you may find in the Testing :: Marionette component in Bugzilla. You can view a list of current bugs to see if your problem is already being addressed.