I'm able to add new entries with xfconf-query but I cannot do that with the GUI tool -- the "new" button is *always* inactive.
See bug #3800 for a better pending solution.
Uh, crap, wrong firefox tab. Sorry!
This is correct, it is a feature that did not make it for 4.6. I plan to implement it for 4.8
This is now fixed with my latest work on xfce4-settings-editor.