Modularise firefox and rofi

modules/app/firefox.nix

@@ -0,0 +1,15 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.samfelag.modules.app.firefox;
+in
+{
+  options.samfelag.modules.app.firefox = {
+    enable = lib.mkEnableOption "firefox";
+  };
+  config = lib.mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [
+      firefox
+    ];
+  };
+}