I am on Guix System. Right now, I have access to IceCat from guix and Firefox from nonguix, of which I have GC’ed Firefox, and modified IceCat, sticking to sane privacy defaults (uBlock Origin + LibRedirect + Dark Reader).
Because I have 120GB of storage, and use Nix side-by-side for personal project, there is barely any space for another third-party package manager, as well as the stuff it will download. I use Guix Home, so having another package manager would also be counterproductive to my effort of creating a reproducibile home user configuration.