Do this, and then use Firefox's profiles to have weaker instances without these configs.

Why? Some sites implement then break this, sadly.

I have extremely locked down instances for banks and so on. On Linux I have an icon which lets me easily launch those extra profiles.

I also use user.js, which means I can just drop in changes, and write comments for each config line, and keep it version controlled too. Great for cloning to other devices too.