One of my favourite Firefox extensions is SubmitToTab. SubmitToTab allows you to middle-click or control-click a button and have it open up in a new tab.
Incidentally, it works great with Seraphiel, and some of the recently added features are even better (in my opinion, anyway), when enhanced by SubmitToTab.
One caveat, though: Utopia targets thievery operations, spells, attacks, and messages are directed at the last kingdom selected. Whichever location is being displayed is not taken into account. It’s similar to the cross-posting bug with the forums, though the consequences can potentially be worse. It doesn’t really matter whether or not you’re using Seraphiel there: having multiple kingdoms open in multiple tabs (no matter how they got opened) can cause this sort of problem.