diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index c9eafaaab332..ab9aa16c93d8 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -404,7 +404,11 @@ pref("media.webvtt.regions.enabled", false);
 pref("media.track.enabled", false);
 
 // Whether to enable MediaSource support
+#ifdef RELEASE_BUILD
 pref("media.mediasource.enabled", false);
+#else
+pref("media.mediasource.enabled", true);
+#endif
 
 #ifdef MOZ_WEBSPEECH
 pref("media.webspeech.recognition.enable", false);