$ nixos-rebuild switch
error: The option `firefox' defined in `/etc/nixos/configuration.nix' does not exist.
(use '--show-trace' to show detailed location information)
building Nix...
error: The option `firefox' defined in `/etc/nixos/configuration.nix' does not exist.
(use '--show-trace' to show detailed location information)
building the system configuration...
error: The option `firefox' defined in `/etc/nixos/configuration.nix' does not exist.
(use '--show-trace' to show detailed location information)