I would recommend arkenfox over librewolf, that way you can use an up to date browser, with the same privacy and greater flexibility to enable features you may want (e.g. no letterbox etc).
LibreWolf massively improved it's update schedule and you can disable any feature you dislike. They have a separate page in the normal user-facing settings for disabling stuff like letterboxing, no need to use about:config. It's better for new users, but also just more convenient for power users. Having to explain how to harden Firefox to a new user would not be ideal.
The first thing I do whenever I install anything is to go through the settings. To turn off trackers, analytics and explore the accessibility features.