You will need to install marionette driver.
pip install marionette-driver
You will also need to install the Firefox developer edition
https://www.mozilla.org/en-US/firefox/developer/
You need create a shortcut target the path as below
<path to browser> -marionette
Type about:config in the browser address path and ensure that you have a setting marionette.port set at 2828. If it is missing, then you have to create that setting.
You will need to open up Firefox developer edition browser first with the flag -marionette. After that, you can start to run the script