diff --git a/browser/base/content/test/browser_popupNotification.js b/browser/base/content/test/browser_popupNotification.js
index 1146b5d7cbd..73ccff81e50 100644
--- a/browser/base/content/test/browser_popupNotification.js
+++ b/browser/base/content/test/browser_popupNotification.js
@@ -137,9 +137,6 @@ function basicNotification() {
         case "dismissed":
           self.dismissalCallbackTriggered = true;
           break;
-        case "showing":
-          self.showingCallbackTriggered = true;
-          break;
         case "shown":
           self.shownCallbackTriggered = true;
           break;
@@ -861,27 +858,6 @@ var tests = [
       this.notification1.remove();
       this.notification2.remove();
     }
-  },
-  { // Test #30 - Showing should be able to modify the popup data
-    run: function() {
-      this.notifyObj = new basicNotification();
-      var normalCallback = this.notifyObj.options.eventCallback;
-      this.notifyObj.options.eventCallback = function (eventName) {
-        if (eventName == "showing") {
-          this.mainAction.label = "Alternate Label";
-        }
-        normalCallback.call(this, eventName);
-      };
-      showNotification(this.notifyObj);
-    },
-    onShown: function(popup) {
-      // checkPopup checks for the matching label. Note that this assumes that
-      // this.notifyObj.mainAction is the same as notification.mainAction,
-      // which could be a problem if we ever decided to deep-copy.
-      checkPopup(popup, this.notifyObj);
-      triggerMainCommand(popup);
-    },
-    onHidden: function() { }
   }
 ];
 
@@ -898,7 +874,6 @@ function showNotification(notifyObj) {
 function checkPopup(popup, notificationObj) {
   info("[Test #" + gTestIndex + "] checking popup");
 
-  ok(notificationObj.showingCallbackTriggered, "showing callback was triggered");
   ok(notificationObj.shownCallbackTriggered, "shown callback was triggered");
 
   let notifications = popup.childNodes;
diff --git a/toolkit/modules/PopupNotifications.jsm b/toolkit/modules/PopupNotifications.jsm
index 7290c194abc..a417accc9d5 100644
--- a/toolkit/modules/PopupNotifications.jsm
+++ b/toolkit/modules/PopupNotifications.jsm
@@ -10,7 +10,6 @@ Components.utils.import("resource://gre/modules/Services.jsm");
 
 const NOTIFICATION_EVENT_DISMISSED = "dismissed";
 const NOTIFICATION_EVENT_REMOVED = "removed";
-const NOTIFICATION_EVENT_SHOWING = "showing";
 const NOTIFICATION_EVENT_SHOWN = "shown";
 
 const ICON_SELECTOR = ".notification-anchor-icon";
@@ -522,9 +521,6 @@ PopupNotifications.prototype = {
   _showPanel: function PopupNotifications_showPanel(notificationsToShow, anchorElement) {
     this.panel.hidden = false;
 
-    notificationsToShow.forEach(function (n) {
-      this._fireCallback(n, NOTIFICATION_EVENT_SHOWING);
-    }, this);
     this._refreshPanel(notificationsToShow);
 
     if (this.isPanelOpen && this._currentAnchorElement == anchorElement)