lib/default.nix

@@ -3,6 +3,7 @@
 let
   fs = import ./fs.nix { inherit lib; };
   hosts = import ./hosts.nix { inherit lib; };
+  modules = import ./modules.nix { inherit lib; };
 in
-  fs // hosts
+  fs // hosts // modules
 

lib/modules.nix

@@ -0,0 +1,10 @@
+{ lib }:
+
+rec {
+  makeOverridable =
+    f: origArgs:
+    let
+      origRes = f origArgs;
+    in
+    origRes // { override = newArgs: makeOverridable f (origArgs // newArgs); };
+}

overlays/nixpak/firefox.nix

@@ -2,7 +2,7 @@
 # https://github.com/ryan4yin/nix-config/blob/7deed26cc5a3af2072b8c89a688f265607babc80/hardening/nixpaks/firefox.nix
 # https://github.com/schizofox/schizofox/blob/cdf69b2a445ff12680657a3bd44ce7c406bf2ae6/flake/modules/home-manager/default.nix
 
-{ ... }: final: prev: {
+{ lib, ... }: final: prev: {
   firefox-esr-wrapped = let
     sandboxed-firefox-esr = prev.mkNixPak {
       config = { sloth, ... }: {
@@ -75,5 +75,5 @@
       };
     };
   in
-    sandboxed-firefox-esr.config.env;
+    lib.makeOverridable sandboxed-firefox-esr.config.env;
 }