You can configure Firefox either by deploying a policies.json file or using the Group Policy.
Group Policy Objects (Windows)
Group Policy Objects offer strong enforcement of policy settings, and are recommended for settings in your environment that are not optional and should not be changed by users. For more information, see the article Customizing Firefox Using Group Policy (Windows).
policies.json (Mac, Linux and Windows)
Allows policies to be set, but such that they can be overridden by users. You can enforce settings with policies.json by disabling write access or through a configuration management solution, but Group Policies are the ideal way to ensure compliance. For more information, see the article Customizing Firefox Using policies.json.