Disable plugins button in Firefox

modules/firefox/default.nix

@@ -50,6 +50,7 @@ in
         "browser.startup.homepage" = "${startpage}";
         "toolkit.legacyUserProfileCustomizations.stylesheets" = true;
         "browser.backspace_action" = 0;
+        "extensions.unifiedExtensions.enabled" = false;
       };
       userChrome = builtins.readFile "${firefox-csshacks}/chrome/autohide_toolbox.css";
     };