--- a/browser/base/content/test/popupNotifications/browser_popupNotification.js
+++ b/browser/base/content/test/popupNotifications/browser_popupNotification.js
@@ -208,16 +208,18 @@ var tests = [
   { id: "Test#9",
     run() {
       this.notifyObj = new BasicNotification(this.id);
       this.notifyObj.mainAction = null;
       this.notifyObj.secondaryActions = null;
       this.notification = showNotification(this.notifyObj);
     },
     onShown(popup) {
+      let notification = popup.childNodes[0];
+      is(notification.getAttribute("buttonhighlight"), "true", "default action is highlighted");
       triggerMainCommand(popup);
     },
     onHidden(popup) {
       ok(!this.notifyObj.mainActionClicked, "mainAction was not clicked");
       ok(!this.notifyObj.dismissalCallbackTriggered, "dismissal callback wasn't triggered");
       ok(this.notifyObj.removedCallbackTriggered, "removed callback triggered");
     }
   },
@@ -228,16 +230,17 @@ var tests = [
     run() {
       this.notifyObj = new BasicNotification(this.id);
       this.notifyObj.mainAction = null;
       this.notification = showNotification(this.notifyObj);
     },
     onShown(popup) {
       let notification = popup.childNodes[0];
       is(notification.getAttribute("secondarybuttonhidden"), "true", "secondary button is hidden");
+      is(notification.getAttribute("buttonhighlight"), "true", "default action is highlighted");
       triggerMainCommand(popup);
     },
     onHidden(popup) {
       ok(!this.notifyObj.mainActionClicked, "mainAction was not clicked");
       ok(!this.notifyObj.dismissalCallbackTriggered, "dismissal callback wasn't triggered");
       ok(this.notifyObj.removedCallbackTriggered, "removed callback triggered");
     }
   },

--- a/toolkit/modules/PopupNotifications.jsm
+++ b/toolkit/modules/PopupNotifications.jsm
@@ -782,16 +782,17 @@ PopupNotifications.prototype = {
         popupnotification.setAttribute("buttonhighlight", !n.mainAction.disableHighlight);
         popupnotification.setAttribute("buttoncommand", "PopupNotifications._onButtonEvent(event, 'buttoncommand');");
         popupnotification.setAttribute("dropmarkerpopupshown", "PopupNotifications._onButtonEvent(event, 'dropmarkerpopupshown');");
         popupnotification.setAttribute("learnmoreclick", "PopupNotifications._onButtonEvent(event, 'learnmoreclick');");
         popupnotification.setAttribute("menucommand", "PopupNotifications._onMenuCommand(event);");
       } else {
         // Enable the default button to let the user close the popup if the close button is hidden
         popupnotification.setAttribute("buttoncommand", "PopupNotifications._onButtonEvent(event, 'buttoncommand');");
+        popupnotification.setAttribute("buttonhighlight", "true");
         popupnotification.removeAttribute("buttonlabel");
         popupnotification.removeAttribute("buttonaccesskey");
         popupnotification.removeAttribute("dropmarkerpopupshown");
         popupnotification.removeAttribute("learnmoreclick");
         popupnotification.removeAttribute("menucommand");
       }
 
       if (n.options.popupIconClass) {