Bug 1535038 - Make dav1d the default AV1 decoder in OSX. r=TD-Linux

Differential Revision: https://phabricator.services.mozilla.com/D23334

--HG--
extra : moz-landing-system : lando

modules/libpref/init/all.js

@@ -661,7 +661,7 @@ pref("media.av1.enabled", true);
 pref("media.av1.use-dav1d", true);
 #elif defined(XP_MACOSX)
 pref("media.av1.enabled", true);
-pref("media.av1.use-dav1d", false);
+pref("media.av1.use-dav1d", true);
 #else
 pref("media.av1.enabled", false);
 pref("media.av1.use-dav1d", false);