Bug 622470 - "Decode on draw must be enabled for Mobile Fennec" [r=mark.finkle]

mobile/app/mobile.js

@@ -582,3 +582,9 @@ pref("indexedDB.feature.enabled", false);
 // prevent video elements from preloading too much data
 pref("media.preload.default", 1); // default to preload none
 pref("media.preload.auto", 2);    // preload metadata if preload=auto
+
+// optimize images memory usage
+pref("image.mem.decodeondraw", true);
+pref("content.image.allow_locking", false);
+pref("image.mem.min_discard_timeout_ms", 20000);
+