--- a/browser/components/search/content/search-one-offs.js
+++ b/browser/components/search/content/search-one-offs.js
@@ -553,18 +553,18 @@ class SearchOneOffs {
 
     let engines = gBrowser.selectedBrowser.engines;
     let tooManyEngines = engines.length > this._addEngineMenuThreshold;
 
     if (tooManyEngines) {
       // Make the top-level menu button.
       let button = document.createXULElement("toolbarbutton");
       list.appendChild(button);
-      button.classList.add("addengine-item", "badged-button");
-      button.setAttribute("class", "addengine-menu-button");
+      button.classList.add("addengine-menu-button", "addengine-item",
+                           "badged-button");
       button.setAttribute("type", "menu");
       button.setAttribute("label",
         this.bundle.GetStringFromName("cmd_addFoundEngineMenu"));
       button.setAttribute("crop", "end");
       button.setAttribute("pack", "start");
 
       // Set the menu button's image to the image of the first engine.  The
       // offered engines may have differing images, so there's no perfect