iMac EFI Firmware Update 1.3
This update fixes several issues to improve the stability of iMac computers.
After the firmware is successfully applied to your Mac, your Boot ROM Version will be:
You can confirm the version of the BootROM installed on your computer using System Profiler.
To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/iMac EFI Firmware Update.app). The updater will launch automatically when the Installer closes.
For more information about firmware updates for Intel-based Macs, please visit: About firmware updates for Intel-based Macs
For additional information, please visit: OS X Mountain Lion: Firmware updates may keep reappearing in the Mac App Store.