diff --git a/modules/firefox.nix b/modules/firefox.nix
index 3c66c7d..962f53e 100644
--- a/modules/firefox.nix
+++ b/modules/firefox.nix
@@ -100,8 +100,8 @@
     DisableProfileImport = true;
   };
 
-  programs.firefox.preferences = {
-    "sidebar.revamp" = true;
-    "sidebar.verticalTabs" = true;
-  };
+  programs.firefox.autoConfig = ''
+    lockPref("sidebar.revamp", true);
+    lockPref("sidebar.verticalTabs", true);
+  '';
 }