There are some extensive details on how to tweak Firefox linked from here.
I added a user.js for myself, and used the tweak to add an option to force new window links to open in the same tab or a new tab. I opted for new tab. The only things I don’t like are that immediately changes focus to the new tab, and that it opens the named comment windows Movable Type blogs normally use in a tab as well, though that second was more unexpected than bad. I’d rather have the same behavior in a single click that I would get from right-click and open in new tab.
I also added the code to banish blinking text, and another one that I promptly forgot.
And finally, I hate it when this happens. Especially when there aren’t backups.