--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -189,17 +189,16 @@
 #include "nsDeviceStorage.h"
 #include "DomainPolicy.h"
 #include "mozilla/dom/ipc/StructuredCloneData.h"
 #include "mozilla/dom/time/DateCacheCleaner.h"
 #include "mozilla/net/NeckoMessageUtils.h"
 #include "mozilla/widget/PuppetBidiKeyboard.h"
 #include "mozilla/RemoteSpellCheckEngineChild.h"
 #include "GMPServiceChild.h"
-#include "GMPDecoderModule.h"
 #include "gfxPlatform.h"
 #include "nscore.h" // for NS_FREE_PERMANENT_DATA
 #include "VRManagerChild.h"
 
 using namespace mozilla;
 using namespace mozilla::docshell;
 using namespace mozilla::dom::devicestorage;
 using namespace mozilla::dom::icc;
@@ -1701,24 +1700,16 @@ ContentChild::RecvNotifyPresentationRece
   NS_WARNING_ASSERTION(service, "presentation service is missing");
 
   Unused << NS_WARN_IF(NS_FAILED(service->UntrackSessionInfo(aSessionId, nsIPresentationService::ROLE_RECEIVER)));
 
   return true;
 }
 
 bool
-ContentChild::RecvNotifyGMPsChanged()
-{
-  GMPDecoderModule::UpdateUsableCodecs();
-  MOZ_ASSERT(NS_IsMainThread());
-  return true;
-}
-
-bool
 ContentChild::RecvNotifyEmptyHTTPCache()
 {
   MOZ_ASSERT(NS_IsMainThread());
   nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
   obs->NotifyObservers(nullptr, "cacheservice:empty-cache", nullptr);
   return true;
 }
 

--- a/dom/ipc/ContentChild.h
+++ b/dom/ipc/ContentChild.h
@@ -355,18 +355,16 @@ public:
 
   virtual bool
   RecvNotifyPresentationReceiverLaunched(PBrowserChild* aIframe,
                                          const nsString& aSessionId) override;
 
   virtual bool
   RecvNotifyPresentationReceiverCleanUp(const nsString& aSessionId) override;
 
-  virtual bool RecvNotifyGMPsChanged() override;
-
   virtual bool RecvNotifyEmptyHTTPCache() override;
 
   virtual PSpeechSynthesisChild* AllocPSpeechSynthesisChild() override;
 
   virtual bool DeallocPSpeechSynthesisChild(PSpeechSynthesisChild* aActor) override;
 
   virtual bool RecvRegisterChrome(InfallibleTArray<ChromePackage>&& packages,
                                   InfallibleTArray<SubstitutionMapping>&& resources,

--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -556,17 +556,16 @@ static const char* sObserverTopics[] = {
 #ifdef MOZ_ENABLE_PROFILER_SPS
   "profiler-started",
   "profiler-stopped",
   "profiler-paused",
   "profiler-resumed",
   "profiler-subprocess-gather",
   "profiler-subprocess",
 #endif
-  "gmp-changed",
   "cacheservice:empty-cache",
 };
 
 // PreallocateAppProcess is called by the PreallocatedProcessManager.
 // ContentParent then takes this process back within
 // GetNewOrPreallocatedAppProcess.
 /*static*/ already_AddRefed<ContentParent>
 ContentParent::PreallocateAppProcess()
@@ -2841,19 +2840,16 @@ ContentParent::Observe(nsISupports* aSub
   }
   else if (!strcmp(aTopic, "profiler-paused")) {
     Unused << SendPauseProfiler(true);
   }
   else if (!strcmp(aTopic, "profiler-resumed")) {
     Unused << SendPauseProfiler(false);
   }
 #endif
-  else if (!strcmp(aTopic, "gmp-changed")) {
-    Unused << SendNotifyGMPsChanged();
-  }
   else if (!strcmp(aTopic, "cacheservice:empty-cache")) {
     Unused << SendNotifyEmptyHTTPCache();
   }
   return NS_OK;
 }
 
 PGMPServiceParent*
 ContentParent::AllocPGMPServiceParent(mozilla::ipc::Transport* aTransport,

--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -624,21 +624,16 @@ child:
 
     /**
      * Notify the child that the info about a presentation receiver needs to be
      * cleaned up.
      */
     async NotifyPresentationReceiverCleanUp(nsString aSessionId);
 
     /**
-     * Notify the child that the Gecko Media Plugins installed changed.
-     */
-    async NotifyGMPsChanged();
-
-    /**
      * Notify the child that cache is emptied.
      */
     async NotifyEmptyHTTPCache();
 
     /**
      * Send a `push` event without data to a service worker in the child.
      */
     async Push(nsCString scope, Principal principal, nsString messageId);