Marionette Python Client

The Marionette Python client library allows you to remotely control a Gecko-based browser or device which is running a Marionette server. This includes Firefox Desktop and Firefox for Android.

The Marionette server is built directly into Gecko and can be started by passing in a command line option to Gecko, or by using a Marionette-enabled build. The server listens for connections from various clients. Clients can then control Gecko by sending commands to the server.

This is the official Python client for Marionette. There also exists a NodeJS client maintained by the Firefox OS automation team.

Getting the Client

The Python client is officially supported. To install it, first make sure you have pip installed then run:

pip install marionette_driver

It’s highly recommended to use virtualenv when installing Marionette to avoid package conflicts and other general nastiness.

You should now be ready to start using Marionette. The best way to learn is to play around with it. Start a Marionette-enabled instance of Firefox, fire up a python shell and follow along with the interactive tutorial!

Using the Client for Testing

Please visit the Marionette Tests section on MDN for information regarding testing with Marionette.

Session Management

A session is a single instance of a Marionette client connected to a Marionette server. Before you can start executing commands, you need to start a session with start_session():

from marionette_driver.marionette import Marionette

client = Marionette('localhost', port=2828)

This returns a session id and an object listing the capabilities of the Marionette server. For example, a server running on Firefox Desktop will have some features which a server running from Firefox Android won’t. It’s also possible to access the capabilities using the session_capabilities attribute. After finishing with a session, you can delete it with delete_session(). Note that this will also happen automatically when the Marionette object is garbage collected.

Context Management

Commands can only be executed in a single window, frame and scope at a time. In order to run commands elsewhere, it’s necessary to explicitly switch to the appropriate context.

Use switch_to_window() to execute commands in the context of a new window:

original_window = client.current_window_handle
for handle in client.window_handles:
    if handle != original_window:
        print("Switched to window with '{}' loaded.".format(client.get_url()))

Similarly, use switch_to_frame() to execute commands in the context of a new frame (e.g an <iframe> element):

iframe = client.find_element(By.TAG_NAME, 'iframe')
assert iframe == client.get_active_frame()

Finally Marionette can switch between chrome and content scope. Chrome is a privileged scope where you can access things like the Firefox UI itself. Content scope is where things like webpages live. You can switch between chrome and content using the set_context() and using_context() functions:

# content scope
with client.using_context(client.CONTEXT_CHROME):
    #chrome scope
    ... do stuff ...
# content scope restored

DOM Elements

In order to inspect or manipulate actual DOM elements, they must first be found using the find_element() or find_elements() methods:

from marionette_driver.marionette import HTMLElement
element = client.find_element(By.ID, 'my-id')
assert type(element) == HTMLElement
elements = client.find_elements(By.TAG_NAME, 'a')
assert type(elements) == list

For a full list of valid search strategies, see Finding Elements.

Now that an element has been found, it’s possible to manipulate it:

For the full list of possible commands, see the HTMLElement reference.

Be warned that a reference to an element object can become stale if it was modified or removed from the document. See Dealing with Stale Elements for tips on working around this limitation.

Script Execution

Sometimes Marionette’s provided APIs just aren’t enough and it is necessary to run arbitrary javascript. This is accomplished with the execute_script() and execute_async_script() functions. They accomplish what their names suggest, the former executes some synchronous JavaScript, while the latter provides a callback mechanism for running asynchronous JavaScript:

result = client.execute_script("return arguments[0] + arguments[1];",
                               script_args=[2, 3])
assert result == 5

The async method works the same way, except it won’t return until a special marionetteScriptFinished() function is called:

result = client.execute_async_script("""
    setTimeout(function() {
      marionetteScriptFinished("all done");
    }, arguments[0]);
""", script_args=[1000])
assert result == "all done"

Beware that running asynchronous scripts can potentially hang the program indefinitely if they are not written properly. It is generally a good idea to set a script timeout using script() and handling ScriptTimeoutException.

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