diff --git a/content/events/public/EventTarget.h b/content/events/public/EventTarget.h
index 1c6c672f7241..d4d85c69f8fb 100644
--- a/content/events/public/EventTarget.h
+++ b/content/events/public/EventTarget.h
@@ -11,12 +11,15 @@
 #include "nsIDOMEventListener.h"
 #include "mozilla/ErrorResult.h"
 #include "mozilla/dom/Nullable.h"
+#include "nsIAtom.h"
+
 class nsDOMEvent;
 
 namespace mozilla {
 namespace dom {
 
 class EventListener;
+class EventHandlerNonNull;
 
 // IID for the dom::EventTarget interface
 #define NS_EVENTTARGET_IID \
@@ -43,6 +46,24 @@ public:
                                    bool aCapture,
                                    ErrorResult& aRv);
   bool DispatchEvent(nsDOMEvent& aEvent, ErrorResult& aRv);
+
+  EventHandlerNonNull* GetEventHandler(const nsAString& aType)
+  {
+    nsCOMPtr<nsIAtom> type = do_GetAtom(aType);
+    return GetEventHandler(type);
+  }
+
+  void SetEventHandler(const nsAString& aType, EventHandlerNonNull* aHandler,
+                       ErrorResult& rv)
+  {
+    nsCOMPtr<nsIAtom> type = do_GetAtom(aType);
+    return SetEventHandler(type, aHandler, rv);
+  }
+
+protected:
+  EventHandlerNonNull* GetEventHandler(nsIAtom* aType);
+  void SetEventHandler(nsIAtom* aType, EventHandlerNonNull* aHandler,
+                       ErrorResult& rv);
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(EventTarget, NS_EVENTTARGET_IID)
diff --git a/content/events/src/EventTarget.cpp b/content/events/src/EventTarget.cpp
index beae68758bca..befa0b39594e 100644
--- a/content/events/src/EventTarget.cpp
+++ b/content/events/src/EventTarget.cpp
@@ -22,5 +22,19 @@ EventTarget::RemoveEventListener(const nsAString& aType,
   }
 }
 
+EventHandlerNonNull*
+EventTarget::GetEventHandler(nsIAtom* aType)
+{
+  nsEventListenerManager* elm = GetListenerManager(false);
+  return elm ? elm->GetEventHandler(aType) : nullptr;
+}
+
+void
+EventTarget::SetEventHandler(nsIAtom* aType, EventHandlerNonNull* aHandler,
+                             ErrorResult& rv)
+{
+  rv = GetListenerManager(true)->SetEventHandler(aType, aHandler);
+}
+
 } // namespace dom
 } // namespace mozilla
diff --git a/content/events/src/nsDOMEventTargetHelper.h b/content/events/src/nsDOMEventTargetHelper.h
index a5868cdf7462..2740e73db052 100644
--- a/content/events/src/nsDOMEventTargetHelper.h
+++ b/content/events/src/nsDOMEventTargetHelper.h
@@ -90,20 +90,11 @@ public:
   nsresult SetEventHandler(nsIAtom* aType,
                            JSContext* aCx,
                            const JS::Value& aValue);
-  void SetEventHandler(nsIAtom* aType,
-                       mozilla::dom::EventHandlerNonNull* aHandler,
-                       mozilla::ErrorResult& rv)
-  {
-    rv = GetListenerManager(true)->SetEventHandler(aType, aHandler);
-  }
+  using mozilla::dom::EventTarget::SetEventHandler;
   void GetEventHandler(nsIAtom* aType,
                        JSContext* aCx,
                        JS::Value* aValue);
-  mozilla::dom::EventHandlerNonNull* GetEventHandler(nsIAtom* aType)
-  {
-    nsEventListenerManager* elm = GetListenerManager(false);
-    return elm ? elm->GetEventHandler(aType) : nullptr;
-  }
+  using mozilla::dom::EventTarget::GetEventHandler;
 
   nsresult CheckInnerWindowCorrectness()
   {
diff --git a/dom/webidl/EventTarget.webidl b/dom/webidl/EventTarget.webidl
index c0b83a4ff790..2ead21ac25d6 100644
--- a/dom/webidl/EventTarget.webidl
+++ b/dom/webidl/EventTarget.webidl
@@ -27,3 +27,13 @@ interface EventTarget {
   [Throws]
   boolean dispatchEvent(Event event);
 };
+
+// Mozilla extensions for use by JS-implemented event targets to
+// implement on* properties.
+partial interface EventTarget {
+  [ChromeOnly, Throws]
+  void setEventHandler(DOMString type, EventHandler handler);
+
+  [ChromeOnly]
+  EventHandler getEventHandler(DOMString type);
+};
diff --git a/dom/workers/EventTarget.h b/dom/workers/EventTarget.h
index ead1d62610f8..077cb94e521f 100644
--- a/dom/workers/EventTarget.h
+++ b/dom/workers/EventTarget.h
@@ -63,6 +63,17 @@ public:
   {
     return mListenerManager.HasListeners();
   }
+
+  void SetEventHandler(JSContext*, const nsAString& aType, JSObject* aHandler,
+                       ErrorResult& rv)
+  {
+    rv.Throw(NS_ERROR_NOT_IMPLEMENTED);
+  }
+
+  JSObject* GetEventHandler(JSContext*, const nsAString& aType)
+  {
+    return nullptr;
+  }
 };
 
 END_WORKERS_NAMESPACE