How to disable Private Browsing in Safari on a 10.8.3 without Xcode
I use OS X 10.8.5 and have Xcode Version 4.6.2 (4H1003) installed.  I just checked the available downloads at Apple Developer in the Member Center and many past versions of Xcode are available for download, as far back as version 2.3.  If you don't have an account I believe you can still create a free account. Although you'll not have access to all downloads like a paid account nonetheless you can download Xcode and related Command Line Tools and much more.

BTW If you're wanting Xcode to edit the MainMenu.nib, don't waste your time as it's compiled and not editable.