Do you happen to use 7 without DWM?
Nope, I'm on Windows 8.1 stock.
Oh, I didn't mess it up. about:config is technically new, however it's the classic version that has been around for ages and was replaced somewhere in 7x/8x. about:confignew is the new version that replaced it somewhere in 7x/8x.
OK I misunderstood it, I expected confignew to be your new implementation.
BTW, there are some options missing in Privacy & Security:
Privacy-R3dfox.png (18.85 KiB) Viewed 520 times
While there are present in LibreWolf and Firefox ESR:
Privacy-Librewolf.png (26.17 KiB) Viewed 520 times
Firefox Relay email, Windows single sign-on and Save and fill adresses. Not that I'm using them but I wonder if it's done on purpose or not.