Yes, you're right, hardcoding "pm_display" would behave like _blank, not like _new. However if I (debian FF) middle-click on any of the four links you provided, they each open in separate new tabs, or if I control-click on any of the four of them, they each open in a separate new windows so that with the _new I can open anywhere except in the current window or in a frame while with pm_display I can open anywhere except the current window (and even there if the current window is in a frame name pm_display).