--- a/dom/media/MediaPrefs.h
+++ b/dom/media/MediaPrefs.h
@@ -165,17 +165,21 @@ private:
   // Flac
   DECL_MEDIA_PREF("media.ogg.flac.enabled",                   FlacInOgg, bool, false);
   DECL_MEDIA_PREF("media.flac.enabled",                       FlacEnabled, bool, true);
 
 #if !defined(RELEASE_OR_BETA)
   DECL_MEDIA_PREF("media.rust.test_mode",                     RustTestMode, bool, false);
 #endif
 
+#if defined(OS_LINUX) && defined(DEBUG)
+  DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, true);
+#else
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, false);
+#endif
 
 public:
   // Manage the singleton:
   static MediaPrefs& GetSingleton();
   static bool SingletonExists();
 
 private:
   template<class T> friend class StaticAutoPtr;