Just downloaded MAMP 1.8.4, copied it to the Applications directory and started it up. The Preferences… button did nothing when I clicked on it. I found a post on forum.mamp.info that shared my pain. The solution: Delete the plist files for MAMP. Easy-peasy, lemon-squeezy.
Thanks Dirk Einecke of the MAMP-Team
http://forum.mamp.info/viewtopic.php?f=2&t=7441
/Users/YOURUSERNAME/Library/Preferences/de.appsolute.MAMP.plist
/Users/YOURUSERNAME/Library/Preferences/de.appsolute.mamppro.plist
/Users/YOURUSERNAME/Library/Preferences/com.living-e.MAMP.plist
/Users/YOURUSERNAME/Library/Preferences/de.living-e_to_appsolute.mampro.plist
/Users/YOURUSERNAME/Library/Preferences/de.living-e.mamppro.plist