vczilla discovered a solution to one of OS X’s most vexing features: When you summon Help in almost any Mac app, the Help Viewer window floats on top of every other open window. Even if you switch from the Help Viewer to another app, the Viewer window stays on top. This can be a real hassle.
Fortunately, it’s possible to switch the Help Viewer to what’s called Dev Mode, which makes its window behave like any other window in OS X—if you switch to another app, the Help Viewer will recede into the background. To make that happen, open Terminal and at the command line type
defaults write com.apple.helpviewer DevMode -bool true, then press Return. The next time you open the Help Viewer, it will no longer float on top of your other windows.
To return to the default behavior, enter
defaults delete com.apple.helpviewer DevMode.