--- a/dom/media/mediasource/MediaSource.cpp
+++ b/dom/media/mediasource/MediaSource.cpp
@@ -1,16 +1,19 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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 "MediaSource.h"
 
+#if MOZ_AV1
+#include "AOMDecoder.h"
+#endif
 #include "AsyncEventRunner.h"
 #include "DecoderTraits.h"
 #include "Benchmark.h"
 #include "DecoderDoctorDiagnostics.h"
 #include "MediaContainerType.h"
 #include "MediaResult.h"
 #include "MediaSourceDemuxer.h"
 #include "MediaSourceUtils.h"
@@ -113,16 +116,21 @@ MediaSource::IsTypeSupported(const nsASt
       return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
     }
     return NS_OK;
   }
   if (mimeType == MEDIAMIMETYPE("video/webm")) {
     if (!(Preferences::GetBool("media.mediasource.webm.enabled", false) ||
           containerType->ExtendedType().Codecs().Contains(
             NS_LITERAL_STRING("vp8")) ||
+#ifdef MOZ_AV1
+          // FIXME: Temporary comparison with the full codecs attribute.
+          // See bug 1377015.
+          AOMDecoder::IsSupportedCodec(containerType->ExtendedType().Codecs().AsString()) ||
+#endif
           IsWebMForced(aDiagnostics))) {
       return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
     }
     return NS_OK;
   }
   if (mimeType == MEDIAMIMETYPE("audio/webm")) {
     if (!(Preferences::GetBool("media.mediasource.webm.enabled", false) ||
           Preferences::GetBool("media.mediasource.webm.audio.enabled", true))) {