QuickLook was added to Mac OS X in Leopard, and it carried over to Snow Leopard mostly unchanged. I don’t use it much, but when I read about this tip, I knew those who do use it would appreciate it.
When you click on a folder and go into QuickLook by pressing the space bar, you’ll see a nice high-resolution image of the folder’s icon. There’s not indication of what’s actually inside though. This tip enables “X-Ray Mode” that shows a preview of a folder’s content in QuickLook.
As always, be sure you have a full backup before proceeding.
Open up Terminal from Macintosh HD/Applications/Utilities and paste in the following:
defaults write com.apple.finder QLEnableXRayFolders 1
And press return. Once this is done, you’ll need to relaunch the Finder for changes to take effect. This is most easily done by selecting Force Quit from the Apple menu, clicking on Finder, and then clicking on the Relaunch button. Once the Finder is relaunched, you can test out this new functionality by clicking on any folder and pressing the space bar.