mkFirefoxModule: add warning for dropped options on wrapped packages

Warns only if the package lacks a `cfg` override and relevant options are configured.

References
https://github.com/nix-community/home-manager/pull/9486

modules/programs/firefox/mkFirefoxModule.nix

@@ -195,14 +195,20 @@ let
     if package == null then
       null
     else if isWrapped then
-      package.override (
-        old:
-        lib.optionalAttrs (lib.functionArgs package.override ? cfg) {
+      if lib.functionArgs package.override ? cfg then
+        package.override (old: {
           cfg = old.cfg or { } // fcfg;
           extraPolicies = (old.extraPolicies or { }) // cfg.policies;
           pkcs11Modules = (old.pkcs11Modules or [ ]) ++ cfg.pkcs11Modules;
-        }
-      )
+        })
+      else
+        let
+          droppedPolicies = cfg.policies != { } && (!isDarwin || cfg.darwinDefaultsId == null);
+          droppedOptions = droppedPolicies || cfg.pkcs11Modules != [ ] || cfg.enableGnomeExtensions;
+        in
+        lib.warnIf droppedOptions
+          "${moduleName}: '${browserName}' cannot be reconfigured; 'policies', 'pkcs11Modules', and 'enableGnomeExtensions' will not be applied."
+          package
     else
       (pkgs.wrapFirefox.override { config = bcfg; }) package { };