--- a/dom/interfaces/push/nsIPushNotifier.idl
+++ b/dom/interfaces/push/nsIPushNotifier.idl
@@ -1,32 +1,62 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsISupports.idl"
 
+%{C++
+#include "nsTArray.h"
+#include "mozilla/Maybe.h"
+
+#define PUSHNOTIFIER_CONTRACTID \
+  "@mozilla.org/push/Notifier;1"
+
+// These constants are duplicated in `PushComponents.js`.
+#define OBSERVER_TOPIC_PUSH "push-message"
+#define OBSERVER_TOPIC_SUBSCRIPTION_CHANGE "push-subscription-change"
+#define OBSERVER_TOPIC_SUBSCRIPTION_LOST "push-subscription-lost"
+%}
+
 interface nsIPrincipal;
 
+[ref] native MaybeData(const mozilla::Maybe<nsTArray<uint8_t>>);
+
 /**
  * Fires service worker events for push messages sent to content subscriptions,
  * and XPCOM observer notifications for system subscriptions.
  */
 [scriptable, builtinclass, uuid(b00dfdeb-14e5-425b-adc7-b531442e3216)]
 interface nsIPushNotifier : nsISupports
 {
+  /**
+   * Fires a `push-message` observer notification, and sends a `push` event to
+   * the service worker registered for the |scope|. |messageId| is an opaque ID
+   * used to report errors if the worker fails to handle the message.
+   */
   void notifyPush(in ACString scope, in nsIPrincipal principal,
                   in DOMString messageId);
 
+  /**
+   * Same as `notifyPush`, except the subject of the observer notification
+   * receives an `nsIPushMessage` instance containing the |data|. Service
+   * workers can access the |data| via the `PushMessageData` WebIDL interface.
+   */
   void notifyPushWithData(in ACString scope, in nsIPrincipal principal,
                           in DOMString messageId,
                           [optional] in uint32_t dataLen,
                           [array, size_is(dataLen)] in uint8_t data);
 
+  /**
+   * Fires a `push-subscription-change` observer notification, and sends a
+   * `pushsubscriptionchange` event to the service worker registered for the
+   * |scope|.
+   */
   void notifySubscriptionChange(in ACString scope, in nsIPrincipal principal);
 
   /**
    * Fires a `push-subscription-lost` observer notification. Chrome code can
    * listen for this notification to see when the Push service removes or
    * expires a subscription for the |scope|.
    *
    * This is useful for Dev Tools and debugging add-ons that need to be
@@ -36,16 +66,44 @@ interface nsIPushNotifier : nsISupports
    * |reason| is an `nsIPushErrorReporter` unsubscribe reason. The reason is
    * wrapped in an `nsISupportsPRUint16` and passed as the subject.
    */
   void notifySubscriptionLost(in ACString scope, in nsIPrincipal principal,
                               [optional] in uint16_t reason);
 
   void notifyError(in ACString scope, in nsIPrincipal principal,
                    in DOMString message, in uint32_t flags);
+
+  /**
+   * Internal methods used to fire service worker events and XPCOM observer
+   * notifications. These are not exposed to JavaScript.
+   */
+
+  [noscript, nostdcall]
+  void notifyPushWorkers(in ACString scope,
+                         in nsIPrincipal principal,
+                         in DOMString messageId,
+                         in MaybeData data);
+
+  [noscript, nostdcall]
+  void notifyPushObservers(in ACString scope, in MaybeData data);
+
+  [noscript, nostdcall]
+  void notifySubscriptionChangeWorkers(in ACString scope,
+                                           in nsIPrincipal principal);
+
+  [noscript, nostdcall]
+  void notifySubscriptionChangeObservers(in ACString scope);
+
+  [noscript, nostdcall]
+  void notifySubscriptionLostObservers(in ACString scope, in uint16_t reason);
+
+  [noscript, nostdcall, notxpcom]
+  void notifyErrorWorkers(in ACString scope, in DOMString message,
+                          in uint32_t flags);
 };
 
 /**
  * A push message sent to a system subscription, used as the subject of a
  * `push-message` observer notification. System subscriptions are created by
  * the system principal, and do not use worker events.
  *
  * This interface resembles the `PushMessageData` WebIDL interface.

--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -163,17 +163,17 @@
 #endif
 #include "NuwaChild.h"
 
 #ifdef MOZ_GAMEPAD
 #include "mozilla/dom/GamepadService.h"
 #endif
 
 #ifndef MOZ_SIMPLEPUSH
-#include "mozilla/dom/PushNotifier.h"
+#include "nsIPushNotifier.h"
 #endif
 
 #include "mozilla/dom/File.h"
 #include "mozilla/dom/cellbroadcast/CellBroadcastIPCService.h"
 #include "mozilla/dom/icc/IccChild.h"
 #include "mozilla/dom/mobileconnection/MobileConnectionChild.h"
 #include "mozilla/dom/mobilemessage/SmsChild.h"
 #include "mozilla/dom/devicestorage/DeviceStorageRequestChild.h"
@@ -3262,23 +3262,21 @@ ContentChild::RecvEndDragSession(const b
 }
 
 bool
 ContentChild::RecvPush(const nsCString& aScope,
                        const IPC::Principal& aPrincipal,
                        const nsString& aMessageId)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifyPushObservers(aScope, Nothing());
   Unused << NS_WARN_IF(NS_FAILED(rv));
 
   rv = pushNotifier->NotifyPushWorkers(aScope, aPrincipal,
                                        aMessageId, Nothing());
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
@@ -3287,67 +3285,61 @@ ContentChild::RecvPush(const nsCString& 
 
 bool
 ContentChild::RecvPushWithData(const nsCString& aScope,
                                const IPC::Principal& aPrincipal,
                                const nsString& aMessageId,
                                InfallibleTArray<uint8_t>&& aData)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifyPushObservers(aScope, Some(aData));
   Unused << NS_WARN_IF(NS_FAILED(rv));
 
   rv = pushNotifier->NotifyPushWorkers(aScope, aPrincipal,
                                        aMessageId, Some(aData));
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 bool
 ContentChild::RecvPushSubscriptionChange(const nsCString& aScope,
                                          const IPC::Principal& aPrincipal)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifySubscriptionChangeObservers(aScope);
   Unused << NS_WARN_IF(NS_FAILED(rv));
 
   rv = pushNotifier->NotifySubscriptionChangeWorkers(aScope, aPrincipal);
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 bool
 ContentChild::RecvPushError(const nsCString& aScope, const nsString& aMessage,
                             const uint32_t& aFlags)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
   pushNotifier->NotifyErrorWorkers(aScope, aMessage, aFlags);
 #endif
   return true;
 }
 
 } // namespace dom
 } // namespace mozilla

--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -260,17 +260,17 @@ using namespace mozilla::system;
 #include "nsIProfileSaveEvent.h"
 #endif
 
 #ifdef MOZ_GAMEPAD
 #include "mozilla/dom/GamepadMonitoring.h"
 #endif
 
 #ifndef MOZ_SIMPLEPUSH
-#include "mozilla/dom/PushNotifier.h"
+#include "nsIPushNotifier.h"
 #endif
 
 #ifdef XP_WIN
 #include "mozilla/widget/AudioSession.h"
 #endif
 
 #include "VRManagerParent.h"            // for VRManagerParent
 
@@ -5837,80 +5837,72 @@ ContentParent::StartProfiler(nsIProfiler
 #endif
 }
 
 bool
 ContentParent::RecvNotifyPushObservers(const nsCString& aScope,
                                        const nsString& aMessageId)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifyPushObservers(aScope, Nothing());
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 bool
 ContentParent::RecvNotifyPushObserversWithData(const nsCString& aScope,
                                                const nsString& aMessageId,
                                                InfallibleTArray<uint8_t>&& aData)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifyPushObservers(aScope, Some(aData));
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 bool
 ContentParent::RecvNotifyPushSubscriptionChangeObservers(const nsCString& aScope)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifySubscriptionChangeObservers(aScope);
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 bool
 ContentParent::RecvNotifyPushSubscriptionLostObservers(const nsCString& aScope,
                                                        const uint16_t& aReason)
 {
 #ifndef MOZ_SIMPLEPUSH
-  nsCOMPtr<nsIPushNotifier> pushNotifierIface =
+  nsCOMPtr<nsIPushNotifier> pushNotifier =
       do_GetService("@mozilla.org/push/Notifier;1");
-  if (NS_WARN_IF(!pushNotifierIface)) {
+  if (NS_WARN_IF(!pushNotifier)) {
       return true;
   }
-  PushNotifier* pushNotifier =
-    static_cast<PushNotifier*>(pushNotifierIface.get());
 
   nsresult rv = pushNotifier->NotifySubscriptionLostObservers(aScope, aReason);
   Unused << NS_WARN_IF(NS_FAILED(rv));
 #endif
   return true;
 }
 
 } // namespace dom

--- a/dom/push/PushNotifier.h
+++ b/dom/push/PushNotifier.h
@@ -5,73 +5,41 @@
 #ifndef mozilla_dom_PushNotifier_h
 #define mozilla_dom_PushNotifier_h
 
 #include "nsIPushNotifier.h"
 
 #include "nsCycleCollectionParticipant.h"
 #include "nsIPrincipal.h"
 #include "nsString.h"
-#include "nsTArray.h"
-
-#include "mozilla/Maybe.h"
-
-#define PUSHNOTIFIER_CONTRACTID \
-  "@mozilla.org/push/Notifier;1"
-
-// These constants are duplicated in `PushComponents.js`.
-#define OBSERVER_TOPIC_PUSH "push-message"
-#define OBSERVER_TOPIC_SUBSCRIPTION_CHANGE "push-subscription-change"
-#define OBSERVER_TOPIC_SUBSCRIPTION_LOST "push-subscription-lost"
 
 namespace mozilla {
 namespace dom {
 
-class ContentParent;
-class ContentChild;
-
 /**
  * `PushNotifier` implements the `nsIPushNotifier` interface. This service
+ * broadcasts XPCOM observer notifications for incoming push messages, then
  * forwards incoming push messages to service workers running in the content
- * process, and emits XPCOM observer notifications for system subscriptions.
- *
- * This service exists solely to support `PushService.jsm`. Other callers
- * should use `ServiceWorkerManager` directly.
+ * process.
  */
 class PushNotifier final : public nsIPushNotifier
 {
-  friend class ContentParent;
-  friend class ContentChild;
-
 public:
   PushNotifier();
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(PushNotifier, nsIPushNotifier)
   NS_DECL_NSIPUSHNOTIFIER
 
 private:
   virtual ~PushNotifier();
 
   nsresult NotifyPush(const nsACString& aScope, nsIPrincipal* aPrincipal,
                       const nsAString& aMessageId,
                       const Maybe<nsTArray<uint8_t>>& aData);
-  nsresult NotifyPushWorkers(const nsACString& aScope,
-                             nsIPrincipal* aPrincipal,
-                             const nsAString& aMessageId,
-                             const Maybe<nsTArray<uint8_t>>& aData);
-  nsresult NotifySubscriptionChangeWorkers(const nsACString& aScope,
-                                           nsIPrincipal* aPrincipal);
-  void NotifyErrorWorkers(const nsACString& aScope, const nsAString& aMessage,
-                          uint32_t aFlags);
-  nsresult NotifyPushObservers(const nsACString& aScope,
-                               const Maybe<nsTArray<uint8_t>>& aData);
-  nsresult NotifySubscriptionChangeObservers(const nsACString& aScope);
-  nsresult NotifySubscriptionLostObservers(const nsACString& aScope,
-                                           uint16_t aReason);
   nsresult DoNotifyObservers(nsISupports *aSubject, const char *aTopic,
                              const nsACString& aScope);
   bool ShouldNotifyWorkers(nsIPrincipal* aPrincipal);
 };
 
 /**
  * `PushMessage` implements the `nsIPushMessage` interface, similar to
  * the `PushMessageData` WebIDL interface. Instances of this class are
@@ -83,20 +51,19 @@ class PushMessage final : public nsIPush
 public:
   explicit PushMessage(const nsTArray<uint8_t>& aData);
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(PushMessage,
                                            nsIPushMessage)
   NS_DECL_NSIPUSHMESSAGE
 
-protected:
+private:
   virtual ~PushMessage();
 
-private:
   nsresult EnsureDecodedText();
 
   nsTArray<uint8_t> mData;
   nsString mDecodedText;
 };
 
 } // namespace dom
 } // namespace mozilla