Launch Property List Editor and open the com.apple.finder.plist file (located in ~/Library/Preferences). From the list of properties, find the one called AppleShowAllFiles.

This is the default application for .plist files, which means that if you double-click a .plist file, it should now automatically launch Property List Editor and open.

Learn how to force OS X to show all files in the Finder, including normally hidden Unix files and folders.