Disable Safari 5's Pop-Up Blocker via MCX?§

Hi All,

I need to disable Safari's pop-up blocker. The older way of doing this does not seem to work on Safari 5.1.5 http://macmule.com/2010/09/25/disabling-safaris-pop-up-blocker-from-terminal/

the below works:

defaults write com.apple.Safari com.apple.Safari.ContentPageGroupIdentifier.WebKit2JavaScriptCanOpenWindowsAutomatically -bool YES

But when attempted via MCX nothing seems to be set.. any ideas? (mcx below).

Display Name:   Safari Disable Pop-Up Blocker       
Application Domain: com.apple.safari        
Key Name:   com.apple.Safari.ContentPageGroupIdentifier.WebKit2JavaScriptCanOpenWindowsAutomatically        
Key Type:   boolean     
Key Value:  true