Fix eval warning

In order to support declarative extension configuration,
extension installation has been moved from
programs.firefox.profiles.<profile>.extensions to
programs.firefox.profiels.<profile>.extensions.packages

config/home-manager/firefox.nix

@@ -121,7 +121,7 @@ in
         "widget.use-xdg-desktop-portal.file-picker" = 1;
         # "privacy.resistFingerprinting" = true;
       };
-      extensions = [ catppuccin_pink ];
+      extensions.packages = [ catppuccin_pink ];
       search = {
         force = true;
         engines = {