--- a/content/media/DecoderTraits.cpp
+++ b/content/media/DecoderTraits.cpp
@@ -384,17 +384,17 @@ DecoderTraits::CanHandleMediaType(const 
   if (IsWaveType(nsDependentCString(aMIMEType))) {
     codecList = gWaveCodecs;
     result = CANPLAY_MAYBE;
   }
 #endif
 #ifdef MOZ_WEBM
   if (IsWebMType(nsDependentCString(aMIMEType))) {
     codecList = gWebMCodecs;
-    result = CANPLAY_YES;
+    result = CANPLAY_MAYBE;
   }
 #endif
 #ifdef MOZ_GSTREAMER
   if (GStreamerDecoder::CanHandleMediaType(nsDependentCString(aMIMEType),
                                            aHaveRequestedCodecs ? &aRequestedCodecs : nullptr)) {
     if (aHaveRequestedCodecs)
       return CANPLAY_YES;
     return CANPLAY_MAYBE;

--- a/content/media/test/can_play_type_webm.js
+++ b/content/media/test/can_play_type_webm.js
@@ -1,16 +1,16 @@
 function check_webm(v, enabled) {
   function check(type, expected) {
     is(v.canPlayType(type), enabled ? expected : "no", type);
   }
 
   // WebM types
-  check("video/webm", "probably");
-  check("audio/webm", "probably");
+  check("video/webm", "maybe");
+  check("audio/webm", "maybe");
 
   // Supported Webm codecs
   check("audio/webm; codecs=vorbis", "probably");
   check("video/webm; codecs=vorbis", "probably");
   check("video/webm; codecs=vorbis,vp8", "probably");
   check("video/webm; codecs=vorbis,vp8.0", "probably");
   check("video/webm; codecs=\"vorbis,vp8\"", "probably");
   check("video/webm; codecs=\"vorbis,vp8.0\"", "probably");