--- a/dom/media/DecoderTraits.cpp
+++ b/dom/media/DecoderTraits.cpp
@@ -179,17 +179,17 @@ static char const *const gWebMCodecs[7] 
   "vp9.0",
   "vorbis",
   "opus",
   nullptr
 };
 #endif
 
 /* static */ bool
-DecoderTraits::IsWebMType(const nsACString& aType)
+DecoderTraits::IsWebMTypeAndEnabled(const nsACString& aType)
 {
 #ifdef MOZ_WEBM
   if (!MediaDecoder::IsWebMEnabled()) {
     return false;
   }
 
   return CodecListContains(gWebMTypes, aType);
 #endif
@@ -198,17 +198,17 @@ DecoderTraits::IsWebMType(const nsACStri
 
 #ifdef MOZ_GSTREAMER
 static bool
 IsGStreamerSupportedType(const nsACString& aMimeType)
 {
   if (!MediaDecoder::IsGStreamerEnabled())
     return false;
 
-  if (DecoderTraits::IsWebMType(aMimeType) && !Preferences::GetBool("media.prefer-gstreamer", false))
+  if (DecoderTraits::IsWebMTypeAndEnabled(aMimeType) && !Preferences::GetBool("media.prefer-gstreamer", false))
     return false;
 
   if (IsOggType(aMimeType) && !Preferences::GetBool("media.prefer-gstreamer", false))
     return false;
 
   return GStreamerDecoder::CanHandleMediaType(aMimeType, nullptr);
 }
 #endif
@@ -349,17 +349,17 @@ IsMP4SupportedType(const nsACString& aTy
 {
   // MP4Decoder/Reader is currently used for MSE and mp4 files local playback.
   bool haveAAC, haveMP3, haveH264;
   return MP4Decoder::CanHandleMediaType(aType, aCodecs, haveAAC, haveH264, haveMP3);
 }
 #endif
 
 /* static */ bool
-DecoderTraits::IsMP4Type(const nsACString& aType)
+DecoderTraits::IsMP4TypeAndEnabled(const nsACString& aType)
 {
 #ifdef MOZ_FMP4
   return IsMP4SupportedType(aType);
 #endif
   return false;
 }
 
 static bool
@@ -432,22 +432,22 @@ DecoderTraits::CanHandleCodecsType(const
     codecList = MediaDecoder::IsOpusEnabled() ? gOggCodecsWithOpus : gOggCodecs;
   }
 #ifdef MOZ_WAVE
   if (IsWaveType(nsDependentCString(aMIMEType))) {
     codecList = gWaveCodecs;
   }
 #endif
 #if !defined(MOZ_OMX_WEBM_DECODER)
-  if (IsWebMType(nsDependentCString(aMIMEType))) {
+  if (IsWebMTypeAndEnabled(nsDependentCString(aMIMEType))) {
     codecList = gWebMCodecs;
   }
 #endif
 #ifdef MOZ_FMP4
-  if (IsMP4Type(nsDependentCString(aMIMEType))) {
+  if (IsMP4TypeAndEnabled(nsDependentCString(aMIMEType))) {
     if (IsMP4SupportedType(nsDependentCString(aMIMEType), aRequestedCodecs)) {
       return CANPLAY_YES;
     } else {
       // We can only reach this position if a particular codec was requested,
       // fmp4 is supported and working: the codec must be invalid.
       return CANPLAY_NO;
     }
   }
@@ -527,21 +527,21 @@ DecoderTraits::CanHandleMediaType(const 
   if (IsOggType(nsDependentCString(aMIMEType))) {
     return CANPLAY_MAYBE;
   }
 #ifdef MOZ_WAVE
   if (IsWaveType(nsDependentCString(aMIMEType))) {
     return CANPLAY_MAYBE;
   }
 #endif
-  if (IsMP4Type(nsDependentCString(aMIMEType))) {
+  if (IsMP4TypeAndEnabled(nsDependentCString(aMIMEType))) {
     return CANPLAY_MAYBE;
   }
 #if !defined(MOZ_OMX_WEBM_DECODER)
-  if (IsWebMType(nsDependentCString(aMIMEType))) {
+  if (IsWebMTypeAndEnabled(nsDependentCString(aMIMEType))) {
     return CANPLAY_MAYBE;
   }
 #endif
   if (IsMP3SupportedType(nsDependentCString(aMIMEType))) {
     return CANPLAY_MAYBE;
   }
 #ifdef MOZ_GSTREAMER
   if (GStreamerDecoder::CanHandleMediaType(nsDependentCString(aMIMEType),
@@ -659,17 +659,17 @@ InstantiateDecoder(const nsACString& aTy
 #endif
 #ifdef MOZ_ANDROID_OMX
   if (MediaDecoder::IsAndroidMediaEnabled() &&
       EnsureAndroidMediaPluginHost()->FindDecoder(aType, nullptr)) {
     decoder = new AndroidMediaDecoder(aType);
     return decoder.forget();
   }
 #endif
-  if (DecoderTraits::IsWebMType(aType)) {
+  if (DecoderTraits::IsWebMTypeAndEnabled(aType)) {
     decoder = new WebMDecoder();
     return decoder.forget();
   }
 #ifdef MOZ_DIRECTSHOW
   // Note: DirectShow should come before WMF, so that we prefer DirectShow's
   // MP3 support over WMF's.
   if (IsDirectShowSupportedType(aType)) {
     decoder = new DirectShowDecoder();
@@ -747,17 +747,17 @@ MediaDecoderReader* DecoderTraits::Creat
   } else
 #endif
 #ifdef MOZ_ANDROID_OMX
   if (MediaDecoder::IsAndroidMediaEnabled() &&
       EnsureAndroidMediaPluginHost()->FindDecoder(aType, nullptr)) {
     decoderReader = new AndroidMediaReader(aDecoder, aType);
   } else
 #endif
-  if (IsWebMType(aType)) {
+  if (IsWebMTypeAndEnabled(aType)) {
     decoderReader = Preferences::GetBool("media.format-reader.webm", true) ?
       static_cast<MediaDecoderReader*>(new MediaFormatReader(aDecoder, new WebMDemuxer(aDecoder->GetResource()))) :
       new WebMReader(aDecoder);
   } else
 #ifdef MOZ_DIRECTSHOW
   if (IsDirectShowSupportedType(aType)) {
     decoderReader = new DirectShowReader(aDecoder);
   } else
@@ -787,17 +787,17 @@ bool DecoderTraits::IsSupportedInVideoDo
     IsOggType(aType) ||
 #ifdef MOZ_OMX_DECODER
     // We support the formats in gB2GOnlyTypes only inside WebApps on firefoxOS
     // but not in general web content. Ensure we dont create a VideoDocument
     // when accessing those format URLs directly.
     (IsOmxSupportedType(aType) &&
      !IsB2GSupportOnlyType(aType)) ||
 #endif
-    IsWebMType(aType) ||
+    IsWebMTypeAndEnabled(aType) ||
 #ifdef MOZ_GSTREAMER
     IsGStreamerSupportedType(aType) ||
 #endif
 #ifdef MOZ_ANDROID_OMX
     (MediaDecoder::IsAndroidMediaEnabled() && IsAndroidMediaType(aType)) ||
 #endif
 #ifdef MOZ_FMP4
     IsMP4SupportedType(aType) ||

--- a/dom/media/DecoderTraits.h
+++ b/dom/media/DecoderTraits.h
@@ -65,16 +65,16 @@ public:
   // or false otherwise. Not all platforms support all MIME types, and
   // vice versa.
   static bool IsSupportedInVideoDocument(const nsACString& aType);
 
   // Returns true if we should not start decoder until we receive
   // OnConnected signal. (currently RTSP only)
   static bool DecoderWaitsForOnConnected(const nsACString& aType);
 
-  static bool IsWebMType(const nsACString& aType);
-  static bool IsMP4Type(const nsACString& aType);
+  static bool IsWebMTypeAndEnabled(const nsACString& aType);
+  static bool IsMP4TypeAndEnabled(const nsACString& aType);
 };
 
 } // namespace mozilla
 
 #endif
 

--- a/dom/media/mediasource/MediaSource.cpp
+++ b/dom/media/mediasource/MediaSource.cpp
@@ -83,27 +83,27 @@ IsTypeSupported(const nsAString& aType)
   }
   NS_ConvertUTF16toUTF8 mimeTypeUTF8(mimeType);
 
   nsAutoString codecs;
   bool hasCodecs = NS_SUCCEEDED(parser.GetParameter("codecs", codecs));
 
   for (uint32_t i = 0; gMediaSourceTypes[i]; ++i) {
     if (mimeType.EqualsASCII(gMediaSourceTypes[i])) {
-      if (DecoderTraits::IsMP4Type(mimeTypeUTF8)) {
+      if (DecoderTraits::IsMP4TypeAndEnabled(mimeTypeUTF8)) {
         if (!Preferences::GetBool("media.mediasource.mp4.enabled", false)) {
           return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
         }
         if (hasCodecs &&
             DecoderTraits::CanHandleCodecsType(mimeTypeUTF8.get(),
                                                codecs) == CANPLAY_NO) {
           return NS_ERROR_DOM_INVALID_STATE_ERR;
         }
         return NS_OK;
-      } else if (DecoderTraits::IsWebMType(mimeTypeUTF8)) {
+      } else if (DecoderTraits::IsWebMTypeAndEnabled(mimeTypeUTF8)) {
         if (!Preferences::GetBool("media.mediasource.webm.enabled", false)) {
           return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
         }
         if (hasCodecs &&
             DecoderTraits::CanHandleCodecsType(mimeTypeUTF8.get(),
                                                codecs) == CANPLAY_NO) {
           return NS_ERROR_DOM_INVALID_STATE_ERR;
         }