nix-config/hosts/lemp11/programs.nix

{
  programs = {
    firefox = {
      enable = true;

      languagePacks = [ "en-GB" ];
      preferences = {
        "intl.accept_languages" = "en-GB, en";
        "intl.regional_prefs.use_os_locales" = true;
      };
    };
  };
}