I don't believe so. It was removed because it has the same behavior as simply clicking on the link. It could be done with an addon for Firefox, but I don't believe that there are any addons developed to accomplish this.

Sorry.

It may not be worth looking for an add-on: Firefox adds their items to the bottom section of the menu, which wouldn't be very convenient.

See also:

• http://kb.mozillazine.org/browser.link.open_newwindow
• 1: current tab; 2:new window; 3:new tab;

For links opened via JavaScript you can look at this pref:

• http://kb.mozillazine.org/browser.link.open_newwindow.restriction