--- a/browser/components/customizableui/CustomizableUI.jsm
+++ b/browser/components/customizableui/CustomizableUI.jsm
@@ -3797,17 +3797,17 @@ function XULWidgetSingleWrapper(aWidgetI
     }
     return node.getAttribute("overflowedItem") == "true";
   });
 
   Object.freeze(this);
 }
 
 const LAZY_RESIZE_INTERVAL_MS = 200;
-const OVERFLOW_PANEL_HIDE_DELAY_MS = 500
+const OVERFLOW_PANEL_HIDE_DELAY_MS = 500;
 
 function OverflowableToolbar(aToolbarNode) {
   this._toolbar = aToolbarNode;
   this._collapsed = new Map();
   this._enabled = true;
 
   this._toolbar.setAttribute("overflowable", "true");
   let doc = this._toolbar.ownerDocument;
@@ -4192,23 +4192,23 @@ OverflowableToolbar.prototype = {
     if (aNode.getAttribute("overflowedItem") == "true") {
       return this._list;
     }
     return this._target;
   },
 
   _hideTimeoutId: null,
   _showWithTimeout: function() {
-    this.show();
-    let window = this._toolbar.ownerDocument.defaultView;
-    if (this._hideTimeoutId) {
-      window.clearTimeout(this._hideTimeoutId);
-      this._hideTimeoutId = null;
-    }
-    this._hideTimeoutId = window.setTimeout(() => {
-      if (!this._panel.firstChild.matches(":hover")) {
-        this._panel.hidePopup();
+    this.show().then(function () {
+      let window = this._toolbar.ownerDocument.defaultView;
+      if (this._hideTimeoutId) {
+        window.clearTimeout(this._hideTimeoutId);
       }
-    }, OVERFLOW_PANEL_HIDE_DELAY_MS);
+      this._hideTimeoutId = window.setTimeout(() => {
+        if (!this._panel.firstChild.matches(":hover")) {
+          this._panel.hidePopup();
+        }
+      }, OVERFLOW_PANEL_HIDE_DELAY_MS);
+    }.bind(this));
   },
 };
 
 CustomizableUIInternal.initialize();