It's really nice. When you setup a new system, you don't have to spend hours changing settings, configs, and installing packages. With NixOS, just copy the config file from your old system and then run nixos-rebuild.
I agree. I can only learn languages by having an idea of something that'll excite me. Making a to-do app rarely teaches me anything since I don't have fun doing it.
Firefox actually has a lot of telemetry that's opt-out rather than opt-in, and doesn't have many privacy protections. Librewolf comes with ublock origin (which blocks trackers and annoyances as well as ads), has extreme fingerprinting protection, and has no google stuff out of the box.
Luckily, in 'murica, corporations can freak you over however they like 😎