diff --git a/browser/components/customizableui/CustomizeMode.jsm b/browser/components/customizableui/CustomizeMode.jsm
index 32b7ee77fb0..14bf690bfd5 100644
--- a/browser/components/customizableui/CustomizeMode.jsm
+++ b/browser/components/customizableui/CustomizeMode.jsm
@@ -1905,8 +1905,14 @@ CustomizeMode.prototype = {
       aEvent.dataTransfer.mozGetDataAt(kDragDataTypePrefix + documentId, 0);
 
     let draggedWrapper = document.getElementById("wrapper-" + draggedItemId);
-    draggedWrapper.hidden = false;
-    draggedWrapper.removeAttribute("mousedown");
+
+    // DraggedWrapper might no longer available if a widget node is
+    // destroyed after starting (but before stopping) a drag.
+    if (draggedWrapper) {
+      draggedWrapper.hidden = false;
+      draggedWrapper.removeAttribute("mousedown");
+    }
+
     if (this._dragOverItem) {
       this._cancelDragActive(this._dragOverItem);
       this._dragOverItem = null;