Rewritten the file from scratch.
Synced all the prefs already configured with mozilla.cfg and added new ones (not settable with the .cfg file), such as:
⛔️ Disabled master password creation
⛔️ Disabled set Desktop background
⛔️ Disabled feedback commands
⛔️ Disabled Firefox Studies
⛔️ Disabled profile import
⛔️ Disabled system addon updates
⛔️ Disabled Firefox home (Search, Top Sites, Highlights, Pocket, Snippets)
⛔️ Removed all defaults bookmarks
⛔️ Removed "Bing", "Google", "Twitter" as search engines and set "DuckDuckGo" as deafult (this policy is only available on the ESR.)