--- a/dom/audiochannel/AudioChannelService.cpp
+++ b/dom/audiochannel/AudioChannelService.cpp
@@ -769,16 +769,21 @@ void
 AudioChannelService::SetAudioChannelMuted(nsPIDOMWindow* aWindow,
                                           AudioChannel aAudioChannel,
                                           bool aMuted)
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(aWindow);
   MOZ_ASSERT(aWindow->IsOuterWindow());
 
+  if (aAudioChannel == AudioChannel::System) {
+    // Workaround for bug1183033, system channel type can always playback.
+    return;
+  }
+
   AudioChannelWindow* winData = GetOrCreateWindowData(aWindow);
   winData->mChannels[(uint32_t)aAudioChannel].mMuted = aMuted;
   RefreshAgentsVolume(aWindow);
 }
 
 NS_IMETHODIMP
 AudioChannelService::SetAudioChannelMuted(nsIDOMWindow* aWindow,
                                           unsigned short aAudioChannel,

--- a/dom/audiochannel/AudioChannelService.h
+++ b/dom/audiochannel/AudioChannelService.h
@@ -170,17 +170,20 @@ private:
 
     uint32_t mNumberOfAgents;
   };
 
   struct AudioChannelWindow final
   {
     explicit AudioChannelWindow(uint64_t aWindowID)
       : mWindowID(aWindowID)
-    {}
+    {
+      // Workaround for bug1183033, system channel type can always playback.
+      mChannels[(int16_t)AudioChannel::System].mMuted = false;
+    }
 
     uint64_t mWindowID;
     AudioChannelConfig mChannels[NUMBER_OF_AUDIO_CHANNELS];
 
     // Raw pointer because the AudioChannelAgent must unregister itself.
     nsTObserverArray<AudioChannelAgent*> mAgents;
   };