For reference, here is the link to Mozilla official best practices for enterprise deployment:

https://developer.mozilla.org/en-US/Firefox/Enterprise_deployment

GPO settings for Firefox:

https://sourceforge.net/projects/firefoxadmx/

https://support.olfeo.com/kb/article/2121

https://www.websense.com/content/support/library/web/hosted/getting_started/apply_policy.aspx