--- a/dom/media/platforms/agnostic/AOMDecoder.cpp
+++ b/dom/media/platforms/agnostic/AOMDecoder.cpp
@@ -304,18 +304,17 @@ AOMDecoder::Drain()
   });
 }
 
 
 /* static */
 bool
 AOMDecoder::IsAV1(const nsACString& aMimeType)
 {
-  return aMimeType.EqualsLiteral("video/webm; codecs=av1")
-         || aMimeType.EqualsLiteral("video/av1");
+  return aMimeType.EqualsLiteral("video/av1");
 }
 
 /* static */
 bool
 AOMDecoder::IsSupportedCodec(const nsAString& aCodecType)
 {
   // While AV1 is under development, we describe support
   // for a specific aom commit hash so sites can check

--- a/dom/media/platforms/agnostic/VPXDecoder.cpp
+++ b/dom/media/platforms/agnostic/VPXDecoder.cpp
@@ -20,20 +20,18 @@
 
 namespace mozilla {
 
 using namespace gfx;
 using namespace layers;
 
 static VPXDecoder::Codec MimeTypeToCodec(const nsACString& aMimeType)
 {
-  if (aMimeType.EqualsLiteral("video/webm; codecs=vp8")) {
+  if (aMimeType.EqualsLiteral("video/vp8")) {
     return VPXDecoder::Codec::VP8;
-  } else if (aMimeType.EqualsLiteral("video/webm; codecs=vp9")) {
-    return VPXDecoder::Codec::VP9;
   } else if (aMimeType.EqualsLiteral("video/vp9")) {
     return VPXDecoder::Codec::VP9;
   }
   return VPXDecoder::Codec::Unknown;
 }
 
 static nsresult
 InitContext(vpx_codec_ctx_t* aCtx,
@@ -283,19 +281,17 @@ VPXDecoder::DecodeAlpha(vpx_image_t** aI
   return NS_OK;
 }
 
 /* static */
 bool
 VPXDecoder::IsVPX(const nsACString& aMimeType, uint8_t aCodecMask)
 {
   return ((aCodecMask & VPXDecoder::VP8)
-          && aMimeType.EqualsLiteral("video/webm; codecs=vp8"))
-         || ((aCodecMask & VPXDecoder::VP9)
-             && aMimeType.EqualsLiteral("video/webm; codecs=vp9"))
+          && aMimeType.EqualsLiteral("video/vp8"))
          || ((aCodecMask & VPXDecoder::VP9)
              && aMimeType.EqualsLiteral("video/vp9"));
 }
 
 /* static */
 bool
 VPXDecoder::IsVP8(const nsACString& aMimeType)
 {

--- a/dom/media/webm/WebMDemuxer.cpp
+++ b/dom/media/webm/WebMDemuxer.cpp
@@ -318,23 +318,23 @@ WebMDemuxer::ReadMetadata()
       nestegg_video_params params;
       r = nestegg_track_video_params(context, track, &params);
       if (r == -1) {
         return NS_ERROR_FAILURE;
       }
       mVideoCodec = nestegg_track_codec_id(context, track);
       switch(mVideoCodec) {
         case NESTEGG_CODEC_VP8:
-          mInfo.mVideo.mMimeType = "video/webm; codecs=vp8";
+          mInfo.mVideo.mMimeType = "video/vp8";
           break;
         case NESTEGG_CODEC_VP9:
-          mInfo.mVideo.mMimeType = "video/webm; codecs=vp9";
+          mInfo.mVideo.mMimeType = "video/vp9";
           break;
         case NESTEGG_CODEC_AV1:
-          mInfo.mVideo.mMimeType = "video/webm; codecs=av1";
+          mInfo.mVideo.mMimeType = "video/av1";
           break;
         default:
           NS_WARNING("Unknown WebM video codec");
           return NS_ERROR_FAILURE;
       }
       // Picture region, taking into account cropping, before scaling
       // to the display size.
       unsigned int cropH = params.crop_right + params.crop_left;

--- a/media/webrtc/signaling/src/media-conduit/WebrtcMediaDataDecoderCodec.cpp
+++ b/media/webrtc/signaling/src/media-conduit/WebrtcMediaDataDecoderCodec.cpp
@@ -31,20 +31,20 @@ WebrtcMediaDataDecoder::~WebrtcMediaData
 
 int32_t
 WebrtcMediaDataDecoder::InitDecode(const webrtc::VideoCodec* aCodecSettings,
                                    int32_t aNumberOfCores)
 {
   nsCString codec;
   switch (aCodecSettings->codecType) {
     case webrtc::VideoCodecType::kVideoCodecVP8:
-      codec = "video/webm; codecs=vp8";
+      codec = "video/vp8";
       break;
     case webrtc::VideoCodecType::kVideoCodecVP9:
-      codec = "video/webm; codecs=vp9";
+      codec = "video/vp9";
       break;
     case webrtc::VideoCodecType::kVideoCodecH264:
       codec = "video/avc";
       break;
     default:
       return WEBRTC_VIDEO_CODEC_ERROR;
   }