diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 747780e76d..863e5c42cc 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -463,9 +463,8 @@ pref("media.mediasource.enabled", true);
 pref("media.mediasource.enabled", false);
 #endif
 
-// We support both H.264 and WebM VP8/VP9 over MSE out-of-the-box
 pref("media.mediasource.mp4.enabled", true);
-pref("media.mediasource.webm.enabled", true);
+pref("media.mediasource.webm.enabled", false);
 
 #ifdef MOZ_WEBSPEECH
 pref("media.webspeech.recognition.enable", false);