I've found TargetKiller to be quite useful. I also have a disliking of pages that insist on opening things in new tabs. It's my browser after all.
A sibling post mentioned TabMixPlus. I have avoided this addon since the mid Fx 2.x days as it has become rather bloaty for my liking. TargetKiller and Focus Last Selected Tab add all the tab functionally I want/need for Fx 3.
Any sufficiently advanced bug is indistinguishable from a feature. -- Rich Kulawiec