--- a/browser/modules/FullZoomUI.jsm
+++ b/browser/modules/FullZoomUI.jsm
@@ -93,18 +93,17 @@ let customizationListener = {
   onAreaNodeRegistered(aAreaType, aAreaNode) {
     if (aAreaType == CustomizableUI.AREA_PANEL) {
       updateZoomUI(aAreaNode.ownerGlobal.gBrowser.selectedBrowser);
     }
   }
 };
 customizationListener.onWidgetAdded =
 customizationListener.onWidgetRemoved =
-customizationListener.onWidgetMoved =
-customizationListener.onWidgetInstanceRemoved = function(aWidgetId) {
+customizationListener.onWidgetMoved = function(aWidgetId) {
   if (aWidgetId == "zoom-controls") {
     for (let window of CustomizableUI.windows) {
       updateZoomUI(window.gBrowser.selectedBrowser);
     }
   }
 };
 customizationListener.onWidgetReset =
 customizationListener.onWidgetUndoMove = function(aWidgetNode) {