I heard about it too, but couldn't find it for a while. It's in the preference window, under Advanced>Scripts & Windows. You can pick what you allow JavaScript to do, such as opening windows by themselves, bring windows to the front or back, or even to resize them. It's great.
The tabbed windows panel has a preference of whether or not pop-up windows open in a new window or a new tab. I've messed around with that, but it doesn't seem to actually work.