diff --git a/content/html/content/src/nsHTMLMediaElement.cpp b/content/html/content/src/nsHTMLMediaElement.cpp
index 3cc663cccde9..b11af6f7541a 100644
--- a/content/html/content/src/nsHTMLMediaElement.cpp
+++ b/content/html/content/src/nsHTMLMediaElement.cpp
@@ -2187,6 +2187,11 @@ nsHTMLMediaElement::CanPlayType(const nsAString& aType, nsAString& aResult)
     aResult.AssignLiteral("maybe");
     break;
   }
+
+  LOG(PR_LOG_DEBUG, ("%p CanPlayType(%s) = \"%s\"", this,
+                     NS_ConvertUTF16toUTF8(aType).get(),
+                     NS_ConvertUTF16toUTF8(aResult).get()));
+
   return NS_OK;
 }
 
diff --git a/content/media/test/can_play_type_mpeg.js b/content/media/test/can_play_type_mpeg.js
index 54140844a278..5598044351d5 100644
--- a/content/media/test/can_play_type_mpeg.js
+++ b/content/media/test/can_play_type_mpeg.js
@@ -7,6 +7,14 @@ function check_mp4(v, enabled) {
   check("video/mp4", "maybe");
   check("audio/mp4", "maybe");
   check("audio/mpeg", "maybe");
+  check("audio/mp3", "maybe");
+  check("audio/x-m4a", "maybe");
+
+  // Not the MIME type that other browsers respond to, so we won't either.
+  check("audio/m4a", "");
+  // Only Safari responds affirmatively to "audio/aac",
+  // so we'll let x-m4a cover aac support.
+  check("audio/aac", "");
 
   check("video/mp4; codecs=\"avc1.42E01E, mp4a.40.2\"", "probably");
   check("video/mp4; codecs=\"avc1.42001E, mp4a.40.2\"", "probably");
@@ -22,6 +30,14 @@ function check_mp4(v, enabled) {
   check("video/mp4; codecs=\"avc1.64001E\"", "probably");
   check("video/mp4; codecs=\"avc1.64001F\"", "probably");
 
+  check("audio/mpeg; codecs=\"mp3\"", "probably");
+  check("audio/mpeg; codecs=mp3", "probably");
+
+  check("audio/mp3; codecs=\"mp3\"", "probably");
+  check("audio/mp3; codecs=mp3", "probably");
+
   check("audio/mp4; codecs=\"mp4a.40.2\"", "probably");
   check("audio/mp4; codecs=mp4a.40.2", "probably");
+  check("audio/x-m4a; codecs=\"mp4a.40.2\"", "probably");
+  check("audio/x-m4a; codecs=mp4a.40.2", "probably");
 }
diff --git a/content/media/wmf/WMFDecoder.cpp b/content/media/wmf/WMFDecoder.cpp
index 72767b48970e..72a6544acb62 100644
--- a/content/media/wmf/WMFDecoder.cpp
+++ b/content/media/wmf/WMFDecoder.cpp
@@ -26,19 +26,17 @@ WMFDecoder::GetSupportedCodecs(const nsACString& aType,
       NS_FAILED(LoadDLLs()))
     return false;
 
-  // MP3 is specified to have no codecs in its "type" param:
-  // http://wiki.whatwg.org/wiki/Video_type_parameters#MPEG
-  // So specify an empty codecs list, so that if script specifies 
-  // a "type" param with codecs, it will be reported as not supported
-  // as per the spec.
+  // Assume that if LoadDLLs() didn't fail, we can playback the types that
+  // we know should be supported on Windows 7+ using WMF.
   static char const *const mp3AudioCodecs[] = {
+    "mp3",
     nullptr
   };
-  if (aType.EqualsASCII("audio/mpeg")) {
+  if (aType.EqualsASCII("audio/mpeg") ||
+      aType.EqualsASCII("audio/mp3")) {
     if (aCodecList) {
       *aCodecList = mp3AudioCodecs;
     }
-    // Assume that if LoadDLLs() didn't fail, we can decode MP3.
     return true;
   }
 
@@ -47,7 +45,8 @@ WMFDecoder::GetSupportedCodecs(const nsACString& aType,
     "mp4a.40.2",    // AAC-LC
     nullptr
   };
-  if (aType.EqualsASCII("audio/mp4")) {
+  if (aType.EqualsASCII("audio/mp4") ||
+      aType.EqualsASCII("audio/x-m4a")) {
     if (aCodecList) {
       *aCodecList = aacAudioCodecs;
     }