diff --git a/toolkit/components/extensions/mozIExtensionAPIRequestHandling.idl b/toolkit/components/extensions/mozIExtensionAPIRequestHandling.idl
index c9efbca1aaa0..3bb920f4e4b9 100644
--- a/toolkit/components/extensions/mozIExtensionAPIRequestHandling.idl
+++ b/toolkit/components/extensions/mozIExtensionAPIRequestHandling.idl
@@ -13,6 +13,12 @@ interface mozIExtensionServiceWorkerInfo : nsISupports
   readonly attribute AString scriptURL;
   readonly attribute AString clientInfoId;
 };
+
+[scriptable, builtinclass, uuid(e68e3c19-1b35-4112-8faa-5c5b84086a5b)]
+interface mozIExtensionEventListener : nsISupports
+{
+  void callListener(in Array<jsval> args);
+};
  
 [scriptable, builtinclass, uuid(0fee1c8f-e363-46a6-bd0c-d3c3338e2534)]
 interface mozIExtensionAPIRequest : nsISupports
@@ -53,6 +59,9 @@ interface mozIExtensionAPIRequest : nsISupports
 
   // Set for requests coming from an extension service worker.
   readonly attribute mozIExtensionServiceWorkerInfo serviceWorkerInfo;
+
+  // Set for `addListener`/`removeListener` API requests.
+  readonly attribute mozIExtensionEventListener eventListener;
 };
 
 [scriptable, uuid(59fd4097-d88e-40fd-8664-fedd8ab67ab6)]
diff --git a/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.cpp b/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.cpp
index a5d856cf549f..b17776b33ee1 100644
--- a/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.cpp
+++ b/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.cpp
@@ -56,6 +56,7 @@ NS_IMPL_CYCLE_COLLECTING_ADDREF(ExtensionAPIRequest)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(ExtensionAPIRequest)
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ExtensionAPIRequest)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mEventListener)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSWInfo)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
@@ -65,6 +66,7 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(ExtensionAPIRequest)
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ExtensionAPIRequest)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mEventListener)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mSWInfo)
   tmp->mStack.setUndefined();
   tmp->mArgs.setUndefined();
@@ -200,5 +202,13 @@ ExtensionAPIRequest::GetServiceWorkerInfo(
   return NS_OK;
 }
 
+NS_IMETHODIMP
+ExtensionAPIRequest::GetEventListener(mozIExtensionEventListener** aListener) {
+  MOZ_ASSERT(NS_IsMainThread());
+  NS_ENSURE_ARG_POINTER(aListener);
+  NS_IF_ADDREF(*aListener = mEventListener);
+  return NS_OK;
+}
+
 }  // namespace extensions
 }  // namespace mozilla
diff --git a/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.h b/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.h
index 9eee70e49516..c2355372b71b 100644
--- a/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.h
+++ b/toolkit/components/extensions/webidl-api/ExtensionAPIRequest.h
@@ -7,6 +7,8 @@
 #ifndef mozilla_extensions_ExtensionAPIRequest_h
 #define mozilla_extensions_ExtensionAPIRequest_h
 
+#include "ExtensionEventListener.h"
+
 #include "mozIExtensionAPIRequestHandling.h"
 #include "mozilla/HoldDropJSObjects.h"
 #include "mozilla/dom/ClientInfo.h"
@@ -82,11 +84,17 @@ class ExtensionAPIRequest : public mozIExtensionAPIRequest {
 
   bool ShouldHaveResult() const { return ShouldHaveResult(mRequestType); }
 
+  void SetEventListener(const RefPtr<ExtensionEventListener>& aListener) {
+    MOZ_ASSERT(!mEventListener);
+    mEventListener = aListener;
+  }
+
  private:
   virtual ~ExtensionAPIRequest() {
     mSWClientInfo = Nothing();
     mArgs.setUndefined();
     mStack.setUndefined();
+    mEventListener = nullptr;
     mozilla::DropJSObjects(this);
   };
 
@@ -96,6 +104,9 @@ class ExtensionAPIRequest : public mozIExtensionAPIRequest {
   JS::Heap<JS::Value> mArgs;
   Maybe<dom::ClientInfo> mSWClientInfo;
   RefPtr<ExtensionServiceWorkerInfo> mSWInfo;
+
+  // Only set for addListener/removeListener API requests.
+  RefPtr<ExtensionEventListener> mEventListener;
 };
 
 }  // namespace extensions
diff --git a/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.cpp b/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.cpp
index 740d3eebfa9d..653ae945bb9b 100644
--- a/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.cpp
+++ b/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.cpp
@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "ExtensionAPIRequestForwarder.h"
+#include "ExtensionEventListener.h"
 
 #include "js/Promise.h"
 #include "mozilla/dom/Client.h"
@@ -251,6 +252,7 @@ RequestWorkerRunnable::RequestWorkerRunnable(
 
 void RequestWorkerRunnable::Init(nsIGlobalObject* aGlobal, JSContext* aCx,
                                  const dom::Sequence<JS::Value>& aArgs,
+                                 ExtensionEventListener* aListener,
                                  ErrorResult& aRv) {
   MOZ_ASSERT(dom::IsCurrentThreadRunningWorker());
 
@@ -274,6 +276,7 @@ void RequestWorkerRunnable::Init(nsIGlobalObject* aGlobal, JSContext* aCx,
   }
 
   SerializeCallerStack(aCx);
+  mEventListener = aListener;
 }
 
 void RequestWorkerRunnable::Init(nsIGlobalObject* aGlobal, JSContext* aCx,
@@ -289,7 +292,7 @@ void RequestWorkerRunnable::Init(nsIGlobalObject* aGlobal, JSContext* aCx,
               ExtensionAPIRequestStructuredCloneWrite,
           };
 
-  Init(aGlobal, aCx, aArgs, aRv);
+  Init(aGlobal, aCx, aArgs, /* aListener */ nullptr, aRv);
   if (aRv.Failed()) {
     return;
   }
@@ -378,6 +381,11 @@ already_AddRefed<ExtensionAPIRequest> RequestWorkerRunnable::CreateAPIRequest(
   RefPtr<ExtensionAPIRequest> request = new ExtensionAPIRequest(
       mOuterRequest->GetRequestType(), *mOuterRequest->GetRequestTarget());
   request->Init(mClientInfo, callArgs, callerStackValue);
+
+  if (mEventListener) {
+    request->SetEventListener(mEventListener.forget());
+  }
+
   return request.forget();
 }
 
diff --git a/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.h b/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.h
index 81bc57f765d4..4eb8a9712aae 100644
--- a/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.h
+++ b/toolkit/components/extensions/webidl-api/ExtensionAPIRequestForwarder.h
@@ -83,7 +83,8 @@ class ExtensionAPIRequestForwarder {
  private:
   already_AddRefed<ExtensionAPIRequest> CreateAPIRequest(
       nsIGlobalObject* aGlobal, JSContext* aCx,
-      const dom::Sequence<JS::Value>& aArgs, ErrorResult& aRv);
+      const dom::Sequence<JS::Value>& aArgs, ExtensionEventListener* aListener,
+      ErrorResult& aRv);
 
   APIRequestType mRequestType;
   ExtensionAPIRequestTarget mRequestTarget;
@@ -113,8 +114,28 @@ class RequestWorkerRunnable : public dom::WorkerMainThreadRunnable {
   RequestWorkerRunnable(dom::WorkerPrivate* aWorkerPrivate,
                         ExtensionAPIRequestForwarder* aOuterAPIRequest);
 
+  /**
+   * Init a request runnable for AddListener and RemoveListener API requests
+   * (which do have an event callback callback and do not expect any return
+   * value).
+   */
   void Init(nsIGlobalObject* aGlobal, JSContext* aCx,
-            const dom::Sequence<JS::Value>& aArgs, ErrorResult& aRv);
+            const dom::Sequence<JS::Value>& aArgs,
+            ExtensionEventListener* aListener, ErrorResult& aRv);
+
+  /**
+   * Init a request runnable for CallFunctionNoReturn API requests (which do
+   * do not expect any return value).
+   */
+  void Init(nsIGlobalObject* aGlobal, JSContext* aCx,
+            const dom::Sequence<JS::Value>& aArgs, ErrorResult& aRv) {
+    Init(aGlobal, aCx, aArgs, nullptr, aRv);
+  }
+
+  /**
+   * Init a request runnable for CallAsyncFunction API requests (which do
+   * expect a promise as return value).
+   */
   void Init(nsIGlobalObject* aGlobal, JSContext* aCx,
             const dom::Sequence<JS::Value>& aArgs,
             const RefPtr<dom::Promise>& aPromiseRetval, ErrorResult& aRv);
@@ -150,6 +171,9 @@ class RequestWorkerRunnable : public dom::WorkerMainThreadRunnable {
   Maybe<UniquePtr<dom::SerializedStackHolder>> mStackHolder;
   Maybe<dom::ClientInfo> mClientInfo;
 
+  // Only set for addListener/removeListener API requests.
+  RefPtr<ExtensionEventListener> mEventListener;
+
   // The outer request object is kept alive by the caller for the
   // entire life of the inner worker runnable.
   ExtensionAPIRequestForwarder* mOuterRequest;
diff --git a/toolkit/components/extensions/webidl-api/ExtensionEventListener.cpp b/toolkit/components/extensions/webidl-api/ExtensionEventListener.cpp
new file mode 100644
index 000000000000..1ffeab5d894d
--- /dev/null
+++ b/toolkit/components/extensions/webidl-api/ExtensionEventListener.cpp
@@ -0,0 +1,20 @@
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ExtensionEventListener.h"
+
+#include "nsThreadManager.h"  // NS_IsMainThread
+
+namespace mozilla {
+namespace extensions {
+
+NS_IMETHODIMP ExtensionEventListener::CallListener(
+    const nsTArray<JS::Value>& aArgs) {
+  MOZ_ASSERT(NS_IsMainThread());
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+}  // namespace extensions
+}  // namespace mozilla
diff --git a/toolkit/components/extensions/webidl-api/ExtensionEventListener.h b/toolkit/components/extensions/webidl-api/ExtensionEventListener.h
new file mode 100644
index 000000000000..4eaac47a8858
--- /dev/null
+++ b/toolkit/components/extensions/webidl-api/ExtensionEventListener.h
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_extensions_ExtensionEventListener_h
+#define mozilla_extensions_ExtensionEventListener_h
+
+#include "mozIExtensionAPIRequestHandling.h"
+
+namespace mozilla {
+namespace extensions {
+
+// A class that represents a callback parameter (passed to addListener /
+// removeListener), instances of this class are received by the
+// mozIExtensionAPIRequestHandler as a property of the mozIExtensionAPIRequest.
+// The mozIExtensionEventListener xpcom interface provides methods that allow
+// the mozIExtensionAPIRequestHandler running in the Main Thread to call the
+// underlying callback Function on its owning thread.
+class ExtensionEventListener : public mozIExtensionEventListener {
+ public:
+  NS_DECL_MOZIEXTENSIONEVENTLISTENER
+};
+
+}  // namespace extensions
+}  // namespace mozilla
+
+#endif  // mozilla_extensions_ExtensionEventListener_h
diff --git a/toolkit/components/extensions/webidl-api/moz.build b/toolkit/components/extensions/webidl-api/moz.build
index f7e51cbe2278..5ff9ea8fea22 100644
--- a/toolkit/components/extensions/webidl-api/moz.build
+++ b/toolkit/components/extensions/webidl-api/moz.build
@@ -12,6 +12,7 @@ UNIFIED_SOURCES += [
     "ExtensionAPIRequest.cpp",
     "ExtensionAPIRequestForwarder.cpp",
     "ExtensionBrowser.cpp",
+    "ExtensionEventListener.cpp",
     "ExtensionEventManager.cpp",
 ]