diff --git a/pkgs/applications/networking/browsers/firefox/wrapper.nix b/pkgs/applications/networking/browsers/firefox/wrapper.nix
index 26fb49ef2a3e..390b26a1b9ee 100644
--- a/pkgs/applications/networking/browsers/firefox/wrapper.nix
+++ b/pkgs/applications/networking/browsers/firefox/wrapper.nix
@@ -115,8 +115,7 @@ let
                 };
               }
             ) {} extensions;
-          } //
-          {
+          } // lib.optionalAttrs usesNixExtensions {
             Extensions = {
               Install = lib.foldr (e: ret:
                 ret ++ [ "${e.outPath}/${e.extid}.xpi" ]