If you have a 2011 Mac unless you have a mac PRO you have a EFI Firmware update for your mac. If you have the machines above then you will want to install this update. To do this hit software update or download the files here from Apple Downloads. Here are the improvements you get with this update:

This update improves the reliability of booting from the network, addresses an issue that can prevent HDCP authentication after reboot, and resolves an issue with boot device selection when a USB storage device is hot-plugged.

[Apple Downloads]