flake/home/applications/firefox/default.nix

{pkgs, ...}: {
  programs.firefox = {
    enable = true;
    package = pkgs.firefox.override {
      extraPrefsFiles = [
        (pkgs.fetchurl {
          url = "https://raw.githubusercontent.com/arkenfox/user.js/126.1/user.js";
          hash = "sha256-XRtG0iLKh8uqbeX7Rc2H6VJwZYJoNZPBlAfZEfrSCP4=";
        })
        # FIXME: why I cannot use `[./user-overrides.js]`?
        (pkgs.runCommand "userjs" {} ''
          install -Dm644 ${./user-overrides.js} $out
        '')
      ];
    };
    profiles."default" = {};
  };
}