The EFI update should be available in the Mac App Store for mid-2012 MacBook Airs and can also be downloaded from the Apple Support site.This update fixes a color issue with HDMI displays connected to MacBook Air, resolves an issue with Windows which can prevent MacBook Air from booting properly, and also resolves an issue where unplugging a Thunderbolt device may cause the system to freeze when waking from standby.
Article Link: Apple Releases EFI Firmware Update 2.6 for MacBook Air