User Agent: Mozilla/5.0 (Windows NT 6.1; rv:20.0) Gecko/20100101 Firefox/20.0 Build ID: 20130326150557 Steps to reproduce: Open a new PB window and close all other windows. Open a link from another program (POP Peeper, Outlook). Actual results: Fx always opens the link in a new non-private window regardless of any setting in about:config.
Yes, this is an intentional design choice from bug 829180.
Could you add a setting to allow the user to choose in which mode to open external links? Thanks.