Apple has posted a firmware update ( for the 24-inch LED Cinema Display. It requires Mac OS X 10.6.8 or later.

The update addresses an issue that may cause intermittent display flickering. This firmware will only install on the Apple 24-inch LED Cinema Display when it’s connected to a Thunderbolt-enabled Mac.

Apple says the firmware update may not resolve the flickering issue if a Mini DisplayPort extender cable is used. You can obtain the update via the Software Updates component of Mac OS X’s Systems Preferences app.