--- a/dom/media/DecoderDoctorDiagnostics.cpp
+++ b/dom/media/DecoderDoctorDiagnostics.cpp
@@ -519,16 +519,23 @@ DecoderDoctorDiagnostics::GetDescription
     s += NS_ConvertUTF16toUTF8(mFormat).get();
     s += mCanPlay ? "', can play" : "', cannot play";
     if (mWMFFailedToLoad) {
       s += ", Windows platform decoder failed to load";
     }
     if (mFFmpegFailedToLoad) {
       s += ", Linux platform decoder failed to load";
     }
+    if (mGMPPDMFailedToStartup) {
+      s += ", GMP PDM failed to startup";
+    } else if (!mGMP.IsEmpty()) {
+      s += ", Using GMP '";
+      s += mGMP;
+      s += "'";
+    }
     break;
   case eMediaKeySystemAccessRequest:
     s = "key system='";
     s += NS_ConvertUTF16toUTF8(mKeySystem).get();
     s += mIsKeySystemSupported ? "', supported" : "', not supported";
     switch (mKeySystemIssue) {
     case eUnset:
       break;

--- a/dom/media/DecoderDoctorDiagnostics.h
+++ b/dom/media/DecoderDoctorDiagnostics.h
@@ -62,16 +62,21 @@ public:
   bool CanPlay() const { return mCanPlay; }
 
   void SetWMFFailedToLoad() { mWMFFailedToLoad = true; }
   bool DidWMFFailToLoad() const { return mWMFFailedToLoad; }
 
   void SetFFmpegFailedToLoad() { mFFmpegFailedToLoad = true; }
   bool DidFFmpegFailToLoad() const { return mFFmpegFailedToLoad; }
 
+  void SetGMPPDMFailedToStartup() { mGMPPDMFailedToStartup = true; }
+  bool DidGMPPDMFailToStartup() const { return mGMPPDMFailedToStartup; }
+  void SetGMP(const nsACString& aGMP) { mGMP = aGMP; }
+  const nsACString& GMP() const { return mGMP; }
+
   const nsAString& KeySystem() const { return mKeySystem; }
   bool IsKeySystemSupported() const { return mIsKeySystemSupported; }
   enum KeySystemIssue {
     eUnset,
     eWidevineWithNoWMF
   };
   void SetKeySystemIssue(KeySystemIssue aKeySystemIssue)
   {
@@ -89,16 +94,18 @@ private:
   DiagnosticsType mDiagnosticsType = eUnsaved;
 
   nsString mFormat;
   // True if there is at least one decoder that can play that format.
   bool mCanPlay = false;
 
   bool mWMFFailedToLoad = false;
   bool mFFmpegFailedToLoad = false;
+  bool mGMPPDMFailedToStartup = false;
+  nsCString mGMP;
 
   nsString mKeySystem;
   bool mIsKeySystemSupported = false;
   KeySystemIssue mKeySystemIssue = eUnset;
 };
 
 } // namespace mozilla
 

--- a/dom/media/platforms/PDMFactory.cpp
+++ b/dom/media/platforms/PDMFactory.cpp
@@ -166,16 +166,19 @@ PDMFactory::CreateDecoder(const TrackInf
     // If libraries failed to load, the following loop over mCurrentPDMs
     // will not even try to use them. So we record failures now.
     if (mWMFFailedToLoad) {
       aDiagnostics->SetWMFFailedToLoad();
     }
     if (mFFmpegFailedToLoad) {
       aDiagnostics->SetFFmpegFailedToLoad();
     }
+    if (mGMPPDMFailedToStartup) {
+      aDiagnostics->SetGMPPDMFailedToStartup();
+    }
   }
 
   for (auto& current : mCurrentPDMs) {
     if (!current->SupportsMimeType(aConfig.mMimeType, aDiagnostics)) {
       continue;
     }
     RefPtr<MediaDataDecoder> m =
       CreateDecoderWithPDM(current,
@@ -329,18 +332,20 @@ PDMFactory::CreatePDMs()
   }
 #endif
 
   m = new AgnosticDecoderModule();
   StartupPDM(m);
 
   if (sGMPDecoderEnabled) {
     m = new GMPDecoderModule();
-    StartupPDM(m);
-  }  
+    if (!StartupPDM(m)) {
+      mGMPPDMFailedToStartup = true;
+    }
+  }
 }
 
 bool
 PDMFactory::StartupPDM(PlatformDecoderModule* aPDM)
 {
   if (aPDM && NS_SUCCEEDED(aPDM->Startup())) {
     mCurrentPDMs.AppendElement(aPDM);
     return true;
@@ -356,16 +361,19 @@ PDMFactory::GetDecoder(const nsACString&
     // If libraries failed to load, the following loop over mCurrentPDMs
     // will not even try to use them. So we record failures now.
     if (mWMFFailedToLoad) {
       aDiagnostics->SetWMFFailedToLoad();
     }
     if (mFFmpegFailedToLoad) {
       aDiagnostics->SetFFmpegFailedToLoad();
     }
+    if (mGMPPDMFailedToStartup) {
+      aDiagnostics->SetGMPPDMFailedToStartup();
+    }
   }
 
   RefPtr<PlatformDecoderModule> pdm;
   for (auto& current : mCurrentPDMs) {
     if (current->SupportsMimeType(aMimeType, aDiagnostics)) {
       pdm = current;
       break;
     }

--- a/dom/media/platforms/PDMFactory.h
+++ b/dom/media/platforms/PDMFactory.h
@@ -92,13 +92,14 @@ private:
   static uint32_t sVideoOutputMinimumInterval_ms;
   static bool sDontDelayInputExhausted;
 
   nsTArray<RefPtr<PlatformDecoderModule>> mCurrentPDMs;
   RefPtr<PlatformDecoderModule> mEMEPDM;
 
   bool mWMFFailedToLoad = false;
   bool mFFmpegFailedToLoad = false;
+  bool mGMPPDMFailedToStartup = false;
 };
 
 } // namespace mozilla
 
 #endif /* PDMFactory_h_ */

--- a/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* 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 "GMPDecoderModule.h"
+#include "DecoderDoctorDiagnostics.h"
 #include "GMPAudioDecoder.h"
 #include "GMPVideoDecoder.h"
 #include "MediaDataDecoderProxy.h"
 #include "mozIGeckoMediaPluginService.h"
 #include "nsServiceManagerUtils.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/StaticMutex.h"
 #include "gmp-audio-decode.h"
@@ -50,16 +51,23 @@ GMPDecoderModule::CreateVideoDecoder(con
                                      FlushableTaskQueue* aVideoTaskQueue,
                                      MediaDataDecoderCallback* aCallback,
                                      DecoderDoctorDiagnostics* aDiagnostics)
 {
   if (!aConfig.mMimeType.EqualsLiteral("video/avc")) {
     return nullptr;
   }
 
+  if (aDiagnostics) {
+    const Maybe<nsCString> preferredGMP = PreferredGMP(aConfig.mMimeType);
+    if (preferredGMP.isSome()) {
+      aDiagnostics->SetGMP(preferredGMP.value());
+    }
+  }
+
   RefPtr<MediaDataDecoderProxy> wrapper = CreateDecoderWrapper(aCallback);
   wrapper->SetProxyTarget(new GMPVideoDecoder(aConfig,
                                               aLayersBackend,
                                               aImageContainer,
                                               aVideoTaskQueue,
                                               wrapper->Callback()));
   return wrapper.forget();
 }
@@ -69,16 +77,23 @@ GMPDecoderModule::CreateAudioDecoder(con
                                      FlushableTaskQueue* aAudioTaskQueue,
                                      MediaDataDecoderCallback* aCallback,
                                      DecoderDoctorDiagnostics* aDiagnostics)
 {
   if (!aConfig.mMimeType.EqualsLiteral("audio/mp4a-latm")) {
     return nullptr;
   }
 
+  if (aDiagnostics) {
+    const Maybe<nsCString> preferredGMP = PreferredGMP(aConfig.mMimeType);
+    if (preferredGMP.isSome()) {
+      aDiagnostics->SetGMP(preferredGMP.value());
+    }
+  }
+
   RefPtr<MediaDataDecoderProxy> wrapper = CreateDecoderWrapper(aCallback);
   wrapper->SetProxyTarget(new GMPAudioDecoder(aConfig,
                                               aAudioTaskQueue,
                                               wrapper->Callback()));
   return wrapper.forget();
 }
 
 PlatformDecoderModule::ConversionRequired
@@ -227,12 +242,17 @@ GMPDecoderModule::SupportsMimeType(const
 
   return false;
 }
 
 bool
 GMPDecoderModule::SupportsMimeType(const nsACString& aMimeType,
                                    DecoderDoctorDiagnostics* aDiagnostics) const
 {
-  return SupportsMimeType(aMimeType, PreferredGMP(aMimeType));
+  const Maybe<nsCString> preferredGMP = PreferredGMP(aMimeType);
+  bool rv = SupportsMimeType(aMimeType, preferredGMP);
+  if (rv && aDiagnostics && preferredGMP.isSome()) {
+    aDiagnostics->SetGMP(preferredGMP.value());
+  }
+  return rv;
 }
 
 } // namespace mozilla