Download ZenFone Zoom 4.21.40.74 Marshmallow FirmwareJuly 3, 2016 By Asif Leave a Comment Filed Under: FirmwareAsus has released the official 4.21.40.74 Android 6.0 Marshmallow update for its ZenFone Zoom (ZX551ML) via OTA. You can download the full update package of this firmware here. [Read more…]