I think that even if you want to harden your Firefox you should use mullvad browser (or librewolf) and then harden it a bit if you want

If you’re a bit pro privacy you should use a browser that reset all the cookies at each closes. So it just doesn’t matter if you refused cookies or not. And you should 100% use Ublock Origin. If think that by default (or with some tweakings) it blocks most of the banners but if you’re not happy with only ublock, I suggest you to try I still don’t care about cookies