--- a/dom/locales/en-US/chrome/dom/dom.properties
+++ b/dom/locales/en-US/chrome/dom/dom.properties
@@ -142,16 +142,20 @@ MediaCannotInitializePulseAudio=Unable t
 # LOCALIZATION NOTE: Do not translate "MediaRecorder".
 MediaRecorderMultiTracksNotSupported=MediaRecorder does not support recording multiple tracks of the same type at this time.
 # LOCALIZATION NOTE: %S is the ID of the MediaStreamTrack passed to MediaStream.addTrack(). Do not translate "MediaStreamTrack" and "AudioChannel".
 MediaStreamAddTrackDifferentAudioChannel=MediaStreamTrack %S could not be added since it belongs to a different AudioChannel.
 # LOCALIZATION NOTE: Do not translate "MediaStream", "stop()" and "MediaStreamTrack"
 MediaStreamStopDeprecatedWarning=MediaStream.stop() is deprecated and will soon be removed. Use MediaStreamTrack.stop() instead.
 # LOCALIZATION NOTE: %S is the URL of the web page which is not served on HTTPS and thus is not encrypted and considered insecure.
 MediaEMEInsecureContextDeprecatedWarning=Using Encrypted Media Extensions at %S on an insecure (i.e. non-HTTPS) context is deprecated and will soon be removed. You should consider switching to a secure origin such as HTTPS.
+# LOCALIZATION NOTE: %S is the URL of the web page which is not served on HTTPS and thus is not encrypted and considered insecure.
+MediaEMENoCapabilitiesDeprecatedWarning=Calling navigator.requestMediaKeySystemAccess() (at %S) without passing a candidate MediaKeySystemConfiguration containing audioCapabilities or videoCapabilities is deprecated and will soon become unsupported.
+# LOCALIZATION NOTE: %S is the URL of the web page which is not served on HTTPS and thus is not encrypted and considered insecure.
+MediaEMENoCodecsDeprecatedWarning=Calling navigator.requestMediaKeySystemAccess() (at %S) without passing a candidate MediaKeySystemConfiguration containing audioCapabilities or videoCapabilities without a contentType with a "codecs" string is deprecated and will soon become unsupported.
 # LOCALIZATION NOTE: Do not translate "DOMException", "code" and "name"
 DOMExceptionCodeWarning=Use of DOMException’s code attribute is deprecated. Use name instead.
 # LOCALIZATION NOTE: Do not translate "__exposedProps__"
 NoExposedPropsWarning=Exposing chrome JS objects to content without __exposedProps__ is insecure and deprecated. See https://developer.mozilla.org/en/XPConnect_wrappers for more information.
 # LOCALIZATION NOTE: Do not translate "Mutation Event" and "MutationObserver"
 MutationEventWarning=Use of Mutation Events is deprecated. Use MutationObserver instead.
 # LOCALIZATION NOTE: Do not translate "Components"
 ComponentsWarning=The Components object is deprecated. It will soon be removed.

--- a/dom/media/eme/MediaKeySystemAccess.cpp
+++ b/dom/media/eme/MediaKeySystemAccess.cpp
@@ -32,16 +32,17 @@
 #include "WebMDecoder.h"
 #include "mozilla/StaticPtr.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "nsUnicharUtils.h"
 #include "mozilla/dom/MediaSource.h"
 #ifdef MOZ_WIDGET_ANDROID
 #include "FennecJNIWrappers.h"
 #endif
+#include <functional>
 
 namespace mozilla {
 namespace dom {
 
 NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(MediaKeySystemAccess,
                                       mParent)
 NS_IMPL_CYCLE_COLLECTING_ADDREF(MediaKeySystemAccess)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(MediaKeySystemAccess)
@@ -538,21 +539,23 @@ IsParameterUnrecognized(const nsAString&
       return true;
     }
   }
   return false;
 }
 
 // 3.1.2.3 Get Supported Capabilities for Audio/Video Type
 static Sequence<MediaKeySystemMediaCapability>
-GetSupportedCapabilities(const CodecType aCodecType,
-                         const nsTArray<MediaKeySystemMediaCapability>& aRequestedCapabilities,
-                         const MediaKeySystemConfiguration& aPartialConfig,
-                         const KeySystemConfig& aKeySystem,
-                         DecoderDoctorDiagnostics* aDiagnostics)
+GetSupportedCapabilities(
+  const CodecType aCodecType,
+  const nsTArray<MediaKeySystemMediaCapability>& aRequestedCapabilities,
+  const MediaKeySystemConfiguration& aPartialConfig,
+  const KeySystemConfig& aKeySystem,
+  DecoderDoctorDiagnostics* aDiagnostics,
+  const std::function<void(const char*)>& aDeprecationLogFn)
 {
   // Let local accumulated configuration be a local copy of partial configuration.
   // (Note: It's not necessary for us to maintain a local copy, as we don't need
   // to test whether capabilites from previous calls to this algorithm work with
   // the capabilities currently being considered in this call. )
 
   // Let supported media capabilities be an empty sequence of
   // MediaKeySystemMediaCapability dictionaries.
@@ -655,16 +658,19 @@ GetSupportedCapabilities(const CodecType
 
     // Let media types be the set of codecs and codec constraints specified by
     // parameters. The case-sensitivity of string comparisons is determined by
     // the appropriate RFC or other specification.
     // (Note: codecs array is 'parameter').
 
     // If media types is empty:
     if (codecs.IsEmpty()) {
+      // Log deprecation warning to encourage authors to not do this!
+      aDeprecationLogFn("MediaEMENoCodecsDeprecatedWarning");
+      // TODO: Remove this once we're sure it doesn't break the web.
       // If container normatively implies a specific set of codecs and codec constraints:
       // Let parameters be that set.
       if (isMP4) {
         if (aCodecType == Audio) {
           codecs.AppendElement(EME_CODEC_AAC);
         } else if (aCodecType == Video) {
           codecs.AppendElement(EME_CODEC_H264);
         }
@@ -829,17 +835,18 @@ UnboxSessionTypes(const Optional<Sequenc
   return sessionTypes;
 }
 
 // 3.1.2.2 Get Supported Configuration and Consent
 static bool
 GetSupportedConfig(const KeySystemConfig& aKeySystem,
                    const MediaKeySystemConfiguration& aCandidate,
                    MediaKeySystemConfiguration& aOutConfig,
-                   DecoderDoctorDiagnostics* aDiagnostics)
+                   DecoderDoctorDiagnostics* aDiagnostics,
+                   const std::function<void(const char*)>& aDeprecationLogFn)
 {
   // Let accumulated configuration be a new MediaKeySystemConfiguration dictionary.
   MediaKeySystemConfiguration config;
   // Set the label member of accumulated configuration to equal the label member of
   // candidate configuration.
   config.mLabel = aCandidate.mLabel;
   // If the initDataTypes member of candidate configuration is non-empty, run the
   // following steps:
@@ -936,29 +943,32 @@ GetSupportedConfig(const KeySystemConfig
   }
   // Set the sessionTypes member of accumulated configuration to session types.
   config.mSessionTypes.Construct(Move(sessionTypes));
 
   // If the videoCapabilities and audioCapabilities members in candidate
   // configuration are both empty, return NotSupported.
   // TODO: Most sites using EME still don't pass capabilities, so we
   // can't reject on it yet without breaking them. So add this later.
+  // Log deprecation warning to encourage authors to not do this!
+  aDeprecationLogFn("MediaEMENoCapabilitiesDeprecatedWarning");
 
   // If the videoCapabilities member in candidate configuration is non-empty:
   if (!aCandidate.mVideoCapabilities.IsEmpty()) {
     // Let video capabilities be the result of executing the Get Supported
     // Capabilities for Audio/Video Type algorithm on Video, candidate
     // configuration's videoCapabilities member, accumulated configuration,
     // and restrictions.
     Sequence<MediaKeySystemMediaCapability> caps =
       GetSupportedCapabilities(Video,
                                aCandidate.mVideoCapabilities,
                                config,
                                aKeySystem,
-                               aDiagnostics);
+                               aDiagnostics,
+                               aDeprecationLogFn);
     // If video capabilities is null, return NotSupported.
     if (caps.IsEmpty()) {
       EME_LOG("MediaKeySystemConfiguration (label='%s') rejected; "
               "no supported video capabilities.",
               NS_ConvertUTF16toUTF8(aCandidate.mLabel).get());
       return false;
     }
     // Set the videoCapabilities member of accumulated configuration to video capabilities.
@@ -973,17 +983,18 @@ GetSupportedConfig(const KeySystemConfig
     // Let audio capabilities be the result of executing the Get Supported Capabilities
     // for Audio/Video Type algorithm on Audio, candidate configuration's audioCapabilities
     // member, accumulated configuration, and restrictions.
     Sequence<MediaKeySystemMediaCapability> caps =
       GetSupportedCapabilities(Audio,
                                aCandidate.mAudioCapabilities,
                                config,
                                aKeySystem,
-                               aDiagnostics);
+                               aDiagnostics,
+                               aDeprecationLogFn);
     // If audio capabilities is null, return NotSupported.
     if (caps.IsEmpty()) {
       EME_LOG("MediaKeySystemConfiguration (label='%s') rejected; "
               "no supported audio capabilities.",
               NS_ConvertUTF16toUTF8(aCandidate.mLabel).get());
       return false;
     }
     // Set the audioCapabilities member of accumulated configuration to audio capabilities.
@@ -1047,30 +1058,33 @@ GetSupportedConfig(const KeySystemConfig
   // Return accumulated configuration.
   aOutConfig = config;
 
   return true;
 }
 
 /* static */
 bool
-MediaKeySystemAccess::GetSupportedConfig(const nsAString& aKeySystem,
-                                         const Sequence<MediaKeySystemConfiguration>& aConfigs,
-                                         MediaKeySystemConfiguration& aOutConfig,
-                                         DecoderDoctorDiagnostics* aDiagnostics)
+MediaKeySystemAccess::GetSupportedConfig(
+  const nsAString& aKeySystem,
+  const Sequence<MediaKeySystemConfiguration>& aConfigs,
+  MediaKeySystemConfiguration& aOutConfig,
+  DecoderDoctorDiagnostics* aDiagnostics,
+  const std::function<void(const char*)>& aDeprecationLogFn)
 {
   KeySystemConfig implementation;
   if (!GetKeySystemConfig(aKeySystem, implementation)) {
     return false;
   }
   for (const MediaKeySystemConfiguration& candidate : aConfigs) {
     if (mozilla::dom::GetSupportedConfig(implementation,
                                          candidate,
                                          aOutConfig,
-                                         aDiagnostics)) {
+                                         aDiagnostics,
+                                         aDeprecationLogFn)) {
       return true;
     }
   }
 
   return false;
 }
 
 

--- a/dom/media/eme/MediaKeySystemAccessManager.cpp
+++ b/dom/media/eme/MediaKeySystemAccessManager.cpp
@@ -13,16 +13,18 @@
 #include "mozilla/DetailedPromise.h"
 #ifdef XP_WIN
 #include "mozilla/WindowsVersion.h"
 #endif
 #ifdef XP_MACOSX
 #include "nsCocoaFeatures.h"
 #endif
 #include "nsPrintfCString.h"
+#include "nsContentUtils.h"
+#include "nsIScriptError.h"
 
 namespace mozilla {
 namespace dom {
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MediaKeySystemAccessManager)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
   NS_INTERFACE_MAP_ENTRY(nsIObserver)
 NS_INTERFACE_MAP_END
@@ -160,18 +162,36 @@ MediaKeySystemAccessManager::Request(Det
     // Failed due to user disabling something, send a notification to
     // chrome, so we can show some UI to explain how the user can rectify
     // the situation.
     MediaKeySystemAccess::NotifyObservers(mWindow, aKeySystem, status);
     aPromise->MaybeReject(NS_ERROR_DOM_NOT_SUPPORTED_ERR, message);
     return;
   }
 
+  nsCOMPtr<nsIDocument> doc = mWindow->GetExtantDoc();
+  std::function<void(const char*)> deprecationWarningLogFn =
+    [doc](const char* aMsgName) {
+      EME_LOG("Logging deprecation warning '%s' to WebConsole.", aMsgName);
+      nsString uri;
+      if (doc) {
+        Unused << doc->GetDocumentURI(uri);
+      }
+      const char16_t* params[] = { uri.get() };
+      nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
+                                      NS_LITERAL_CSTRING("Media"),
+                                      doc,
+                                      nsContentUtils::eDOM_PROPERTIES,
+                                      aMsgName,
+                                      params,
+                                      ArrayLength(params));
+    };
   MediaKeySystemConfiguration config;
-  if (MediaKeySystemAccess::GetSupportedConfig(aKeySystem, aConfigs, config, &diagnostics)) {
+  if (MediaKeySystemAccess::GetSupportedConfig(
+        aKeySystem, aConfigs, config, &diagnostics, deprecationWarningLogFn)) {
     RefPtr<MediaKeySystemAccess> access(
       new MediaKeySystemAccess(mWindow, aKeySystem, config));
     aPromise->MaybeResolve(access);
     diagnostics.StoreMediaKeySystemAccess(mWindow->GetExtantDoc(),
                                           aKeySystem, true, __func__);
     return;
   }
   // Not to inform user, because nothing to do if the corresponding keySystem