diff --git a/browser/components/customizableui/src/CustomizableWidgets.jsm b/browser/components/customizableui/src/CustomizableWidgets.jsm
index 0ae0cc6af01..9a35add5a92 100644
--- a/browser/components/customizableui/src/CustomizableWidgets.jsm
+++ b/browser/components/customizableui/src/CustomizableWidgets.jsm
@@ -416,6 +416,11 @@ const CustomizableWidgets = [{
       let zoomResetButton = node.childNodes[2];
       let window = aDocument.defaultView;
       function updateZoomResetButton() {
+        let updateDisplay = true;
+        // Label should always show 100% in customize mode, so don't update:
+        if (aDocument.documentElement.hasAttribute("customizing")) {
+          updateDisplay = false;
+        }
         //XXXgijs in some tests we get called very early, and there's no docShell on the
         // tabbrowser. This breaks the zoom toolkit code (see bug 897410). Don't let that happen:
         let zoomFactor = 100;
@@ -423,7 +428,7 @@ const CustomizableWidgets = [{
           zoomFactor = Math.floor(window.ZoomManager.zoom * 100);
         } catch (e) {}
         zoomResetButton.setAttribute("label", CustomizableUI.getLocalizedProperty(
-          buttons[1], "label", [zoomFactor]
+          buttons[1], "label", [updateDisplay ? zoomFactor : 100]
         ));
       };
 
@@ -508,6 +513,18 @@ const CustomizableWidgets = [{
           container.removeEventListener("TabSelect", updateZoomResetButton);
         }.bind(this),
 
+        onCustomizeStart: function(aWindow) {
+          if (aWindow.document == aDocument) {
+            updateZoomResetButton();
+          }
+        },
+
+        onCustomizeEnd: function(aWindow) {
+          if (aWindow.document == aDocument) {
+            updateZoomResetButton();
+          }
+        },
+
         onWidgetDrag: function(aWidgetId, aArea) {
           if (aWidgetId != this.id)
             return;