Noting the change from the original build it replaces, Apple's EFI firmware update is labeled version 2.9.1 and looks to fix sleep-from-wake issues seen by owners of mid-2011 MacBook Air models.
A day after version 2.9 was released, users reported flaws in the firmware, including installation bugs and problems that led to system crashes. Some users were met with "bricked" laptops after installing the update, which in one case prompted an Apple Store Genius Bar technician to perform a "soft" SMC resets in hopes of removing the tainted EFI build.
Following multiple reports of identical issues posted to its Support Communities forum, Apple pulled the update from its Support Downloads webpage.
As for the new 2.9.1 release, the MacBook Air EFI firmware resolves an issue that causes some mid-2011 models to take longer than expected to wake from sleep and addresses a rare problem that causes the computer's fans to run at full speed after waking from sleep.
Apple's MacBook Air EFI Firmware Update 2.9.1 is available now as a 4.3MB download.