--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -1705,18 +1705,16 @@ ContentChild::RecvNotifyPresentationRece
   return true;
 }
 
 bool
 ContentChild::RecvNotifyGMPsChanged()
 {
   GMPDecoderModule::UpdateUsableCodecs();
   MOZ_ASSERT(NS_IsMainThread());
-  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
-  obs->NotifyObservers(nullptr, "gmp-changed", nullptr);
   return true;
 }
 
 bool
 ContentChild::RecvNotifyEmptyHTTPCache()
 {
   MOZ_ASSERT(NS_IsMainThread());
   nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();

--- a/dom/media/gmp/GMPServiceChild.cpp
+++ b/dom/media/gmp/GMPServiceChild.cpp
@@ -11,16 +11,18 @@
 #include "mozIGeckoMediaPluginChromeService.h"
 #include "nsCOMPtr.h"
 #include "GMPParent.h"
 #include "GMPContentParent.h"
 #include "nsXPCOMPrivate.h"
 #include "mozilla/SyncRunnable.h"
 #include "runnable_utils.h"
 #include "base/task.h"
+#include "nsIObserverService.h"
+#include "nsComponentManagerUtils.h"
 
 namespace mozilla {
 
 #ifdef LOG
 #undef LOG
 #endif
 
 #define LOGD(msg) MOZ_LOG(GetGMPLog(), mozilla::LogLevel::Debug, msg)
@@ -201,16 +203,24 @@ GeckoMediaPluginServiceChild::UpdateGMPC
     ClearOnShutdown(&sGMPCapabilities);
   }
   sGMPCapabilities->Clear();
   for (const GMPCapabilityData& plugin : aCapabilities) {
     sGMPCapabilities->AppendElement(GMPCapabilityAndVersion(plugin));
   }
 
   LOGD(("UpdateGMPCapabilities {%s}", GMPCapabilitiesToString().get()));
+
+  // Fire a notification so that any MediaKeySystemAccess
+  // requests waiting on a CDM to download will retry.
+  nsCOMPtr<nsIObserverService> obsService = mozilla::services::GetObserverService();
+  MOZ_ASSERT(obsService);
+  if (obsService) {
+    obsService->NotifyObservers(nullptr, "gmp-changed", nullptr);
+  }
 }
 
 NS_IMETHODIMP
 GeckoMediaPluginServiceChild::GetPluginVersionForAPI(const nsACString& aAPI,
                                                      nsTArray<nsCString>* aTags,
                                                      bool* aHasPlugin,
                                                      nsACString& aOutVersion)
 {

--- a/dom/media/gmp/GMPServiceParent.cpp
+++ b/dom/media/gmp/GMPServiceParent.cpp
@@ -834,19 +834,16 @@ GeckoMediaPluginServiceParent::PathRunna
 {
   mService->RemoveOnGMPThread(mPath,
                               mOperation == REMOVE_AND_DELETE_FROM_DISK,
                               mDefer);
 
   mService->UpdateContentProcessGMPCapabilities();
 
 #ifndef MOZ_WIDGET_GONK // Bug 1214967: disabled on B2G due to inscrutable test failures.
-  // For e10s, we must fire a notification so that all ContentParents notify
-  // their children to update the codecs that the GMPDecoderModule can use.
-  NS_DispatchToMainThread(new NotifyObserversTask("gmp-changed"), NS_DISPATCH_NORMAL);
   // For non-e10s, and for decoding in the chrome process, must update GMP
   // PDM's codecs list directly.
   NS_DispatchToMainThread(NS_NewRunnableFunction([]() -> void {
     GMPDecoderModule::UpdateUsableCodecs();
   }));
 #endif
   return NS_OK;
 }
@@ -890,16 +887,24 @@ GeckoMediaPluginServiceParent::UpdateCon
         x.capabilities().AppendElement(GMPAPITags(tag.mAPIName, tag.mAPITags));
       }
       caps.AppendElement(Move(x));
     }
   }
   for (auto* cp : ContentParent::AllProcesses(ContentParent::eLive)) {
     Unused << cp->SendGMPsChanged(caps);
   }
+
+  // For non-e10s, we must fire a notification so that any MediaKeySystemAccess
+  // requests waiting on a CDM to download will retry.
+  nsCOMPtr<nsIObserverService> obsService = mozilla::services::GetObserverService();
+  MOZ_ASSERT(obsService);
+  if (obsService) {
+    obsService->NotifyObservers(nullptr, "gmp-changed", nullptr);
+  }
 }
 
 RefPtr<GenericPromise>
 GeckoMediaPluginServiceParent::AsyncAddPluginDirectory(const nsAString& aDirectory)
 {
   RefPtr<AbstractThread> thread(GetAbstractGMPThread());
   if (!thread) {
     return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
@@ -908,23 +913,16 @@ GeckoMediaPluginServiceParent::AsyncAddP
   nsString dir(aDirectory);
   RefPtr<GeckoMediaPluginServiceParent> self = this;
   return InvokeAsync(thread, this, __func__, &GeckoMediaPluginServiceParent::AddOnGMPThread, dir)
     ->Then(AbstractThread::MainThread(), __func__,
       [dir, self]() -> void {
         LOGD(("GeckoMediaPluginServiceParent::AsyncAddPluginDirectory %s succeeded",
               NS_ConvertUTF16toUTF8(dir).get()));
         MOZ_ASSERT(NS_IsMainThread());
-        // For e10s, we must fire a notification so that all ContentParents notify
-        // their children to update the codecs that the GMPDecoderModule can use.
-        nsCOMPtr<nsIObserverService> obsService = mozilla::services::GetObserverService();
-        MOZ_ASSERT(obsService);
-        if (obsService) {
-          obsService->NotifyObservers(nullptr, "gmp-changed", nullptr);
-        }
         self->UpdateContentProcessGMPCapabilities();
         // For non-e10s, and for decoding in the chrome process, must update GMP
         // PDM's codecs list directly.
         GMPDecoderModule::UpdateUsableCodecs();
       },
       [dir]() -> void {
         LOGD(("GeckoMediaPluginServiceParent::AsyncAddPluginDirectory %s failed",
               NS_ConvertUTF16toUTF8(dir).get()));