diff --git a/dom/plugins/base/npapi.h b/dom/plugins/base/npapi.h
index 35146a1b9ff..2c773b096b3 100644
--- a/dom/plugins/base/npapi.h
+++ b/dom/plugins/base/npapi.h
@@ -411,7 +411,9 @@ typedef enum {
   , NPNVsupportsCocoaBool = 3001 /* TRUE if the browser supports the Cocoa event model */
   , NPNVsupportsUpdatedCocoaTextInputBool = 3002 /* TRUE if the browser supports the updated
                                                     Cocoa text input specification. */
+#endif
   , NPNVmuteAudioBool = 4000 /* Request that the browser wants to mute or unmute the plugin */
+#if defined(XP_MACOSX)
   , NPNVsupportsCompositingCoreAnimationPluginsBool = 74656 /* TRUE if the browser supports
                                                                CA model compositing */
 #endif
diff --git a/dom/plugins/base/nsNPAPIPlugin.cpp b/dom/plugins/base/nsNPAPIPlugin.cpp
index 7c2f622c1c8..d677d92fce9 100644
--- a/dom/plugins/base/nsNPAPIPlugin.cpp
+++ b/dom/plugins/base/nsNPAPIPlugin.cpp
@@ -106,6 +106,8 @@ using mozilla::plugins::PluginModuleContentParent;
 #define LOG(args...)  __android_log_print(ANDROID_LOG_INFO, "GeckoPlugins" , ## args)
 #endif
 
+#include "nsIAudioChannelAgent.h"
+
 using namespace mozilla;
 using namespace mozilla::plugins::parent;
 
@@ -2403,23 +2405,42 @@ _setvalue(NPP npp, NPPVariable variable, void *result)
     }
 
     case NPPVpluginIsPlayingAudio: {
-      // For testing, remove me
-      printf("set audio %p\n", result);
-      bool isPlaying = !!result;
+      bool isMuted = !result;
 
-      nsCOMPtr<nsIDocument> doc = GetDocumentFromNPP(npp);
-      if (doc) {
-        nsCOMPtr<nsPIDOMWindow> domwindow = doc->GetWindow();
-        nsCOMPtr<nsIObserverService> observerService =
-          services::GetObserverService();
-        if (observerService) {
-          // XXX THIS NEEDS A BETTER API
-          observerService->NotifyObservers(ToSupports(domwindow),
-                                           "media-playback",
-                                           isPlaying ? NS_LITERAL_STRING("active").get() :
-                                                       NS_LITERAL_STRING("inactive").get());
+      nsNPAPIPluginInstance* inst = (nsNPAPIPluginInstance*) npp->ndata;
+      MOZ_ASSERT(inst);
+
+      if (isMuted && !inst->HasAudioChannelAgent()) {
+        return NPERR_NO_ERROR;
+      }
+
+      nsCOMPtr<nsIAudioChannelAgent> agent;
+      nsresult rv = inst->GetOrCreateAudioChannelAgent(getter_AddRefs(agent));
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return NPERR_NO_ERROR;
+      }
+
+      MOZ_ASSERT(agent);
+
+      if (isMuted) {
+        rv = agent->NotifyStoppedPlaying();
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return NPERR_NO_ERROR;
+        }
+      } else {
+        float volume = 0.0;
+        bool muted = true;
+        rv = agent->NotifyStartedPlaying(&volume, &muted);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return NPERR_NO_ERROR;
+        }
+
+        rv = inst->WindowVolumeChanged(volume, muted);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return NPERR_NO_ERROR;
         }
       }
+
       return NPERR_NO_ERROR;
     }
 
diff --git a/dom/plugins/base/nsNPAPIPluginInstance.cpp b/dom/plugins/base/nsNPAPIPluginInstance.cpp
index 4f35b147ab7..a15a9f20926 100644
--- a/dom/plugins/base/nsNPAPIPluginInstance.cpp
+++ b/dom/plugins/base/nsNPAPIPluginInstance.cpp
@@ -40,6 +40,7 @@
 #include "mozilla/unused.h"
 #include "nsILoadContext.h"
 #include "mozilla/dom/HTMLObjectElementBinding.h"
+#include "AudioChannelService.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -169,7 +170,7 @@ using namespace mozilla::layers;
 
 static NS_DEFINE_IID(kIOutputStreamIID, NS_IOUTPUTSTREAM_IID);
 
-NS_IMPL_ISUPPORTS0(nsNPAPIPluginInstance)
+NS_IMPL_ISUPPORTS(nsNPAPIPluginInstance, nsIAudioChannelAgentCallback)
 
 nsNPAPIPluginInstance::nsNPAPIPluginInstance()
   : mDrawingModel(kDefaultDrawingModel)
@@ -253,6 +254,7 @@ nsNPAPIPluginInstance::Destroy()
 {
   Stop();
   mPlugin = nullptr;
+  mAudioChannelAgent = nullptr;
 
 #if MOZ_WIDGET_ANDROID
   if (mContentSurface)
@@ -1788,3 +1790,71 @@ nsNPAPIPluginInstance::GetRunID(uint32_t* aRunID)
 
   return library->GetRunID(aRunID);
 }
+
+nsresult
+nsNPAPIPluginInstance::GetOrCreateAudioChannelAgent(nsIAudioChannelAgent** aAgent)
+{
+  if (!mAudioChannelAgent) {
+    nsresult rv;
+    mAudioChannelAgent = do_CreateInstance("@mozilla.org/audiochannelagent;1", &rv);
+    if (NS_WARN_IF(!mAudioChannelAgent)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsCOMPtr<nsPIDOMWindow> window = GetDOMWindow();
+    if (NS_WARN_IF(!window)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    rv = mAudioChannelAgent->Init(window->GetCurrentInnerWindow(),
+                                 (int32_t)AudioChannelService::GetDefaultAudioChannel(),
+                                 this);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  nsCOMPtr<nsIAudioChannelAgent> agent = mAudioChannelAgent;
+  agent.forget(aAgent);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsNPAPIPluginInstance::WindowVolumeChanged(float aVolume, bool aMuted)
+{
+  // We just support mute/unmute
+  nsresult rv = SetMuted(aMuted);
+  NS_WARN_IF(NS_FAILED(rv));
+  return rv;
+}
+
+NS_IMETHODIMP
+nsNPAPIPluginInstance::WindowAudioCaptureChanged()
+{
+  return NS_OK;
+}
+
+nsresult
+nsNPAPIPluginInstance::SetMuted(bool aIsMuted)
+{
+  if (RUNNING != mRunning)
+    return NS_OK;
+
+  PLUGIN_LOG(PLUGIN_LOG_NORMAL, ("nsNPAPIPluginInstance informing plugin of mute state change this=%p\n",this));
+
+  if (!mPlugin || !mPlugin->GetLibrary())
+    return NS_ERROR_FAILURE;
+
+  NPPluginFuncs* pluginFunctions = mPlugin->PluginFuncs();
+
+  if (!pluginFunctions->setvalue)
+    return NS_ERROR_FAILURE;
+
+  PluginDestructionGuard guard(this);
+
+  NPError error;
+  NPBool value = static_cast<NPBool>(aIsMuted);
+  NS_TRY_SAFE_CALL_RETURN(error, (*pluginFunctions->setvalue)(&mNPP, NPNVmuteAudioBool, &value), this,
+                          NS_PLUGIN_CALL_UNSAFE_TO_REENTER_GECKO);
+  return (error == NPERR_NO_ERROR) ? NS_OK : NS_ERROR_FAILURE;
+}
diff --git a/dom/plugins/base/nsNPAPIPluginInstance.h b/dom/plugins/base/nsNPAPIPluginInstance.h
index 21d4f312039..157f71b53f0 100644
--- a/dom/plugins/base/nsNPAPIPluginInstance.h
+++ b/dom/plugins/base/nsNPAPIPluginInstance.h
@@ -17,6 +17,7 @@
 #include "nsHashKeys.h"
 #include <prinrval.h>
 #include "js/TypeDecls.h"
+#include "nsIAudioChannelAgent.h"
 #ifdef MOZ_WIDGET_ANDROID
 #include "nsAutoPtr.h"
 #include "nsIRunnable.h"
@@ -74,13 +75,14 @@ public:
   bool needUnschedule;
 };
 
-class nsNPAPIPluginInstance : public nsISupports
+class nsNPAPIPluginInstance final : public nsIAudioChannelAgentCallback
 {
 private:
   typedef mozilla::PluginLibrary PluginLibrary;
 
 public:
   NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIAUDIOCHANNELAGENTCALLBACK
 
   nsresult Initialize(nsNPAPIPlugin *aPlugin, nsPluginInstanceOwner* aOwner, const nsACString& aMIMEType);
   nsresult Start();
@@ -117,6 +119,15 @@ public:
   nsPluginInstanceOwner* GetOwner();
   void SetOwner(nsPluginInstanceOwner *aOwner);
 
+  bool HasAudioChannelAgent() const
+  {
+    return !!mAudioChannelAgent;
+  }
+
+  nsresult GetOrCreateAudioChannelAgent(nsIAudioChannelAgent** aAgent);
+
+  nsresult SetMuted(bool aIsMuted);
+
   nsNPAPIPlugin* GetPlugin();
 
   nsresult GetNPP(NPP * aNPP);
@@ -404,6 +415,8 @@ private:
   uint32_t mCachedParamLength;
   char **mCachedParamNames;
   char **mCachedParamValues;
+
+  nsCOMPtr<nsIAudioChannelAgent> mAudioChannelAgent;
 };
 
 // On Android, we need to guard against plugin code leaking entries in the local