Apple has posted a bugfixed version EFI Firmware Update 2.9 a for MacBook Air (Mid 2011) models. The update addresses an issue where systems may take longer to wake from sleep than expected, and fixes a rare issue that may cause fans to run at full speed after waking from sleep.
Note that you need to have OS X MAvericks installed in order to apply this update. It can be installed via Software Update, or from a downloadable freestanding installer.
OS X 10.9.2 and later
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