WebKit in Apple Safari before 6.1 disables the Private Browsing feature upon a launch of the Web Inspector, which makes it easier for context-dependent attackers to obtain browsing information by leveraging LocalStorage/ files.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-4970
http://lists.apple.com/archives/security-announce/2013/Oct/msg00003.html