This is a GreaseMonkey script to quickly collapse Reddit threads that are under your mouse cursor.
Mousing over any sub-comment in a long chain will draw a faint box-shadow border around the entire thread, providing a stronger visual clue to identify the chain of comments you're on.
Hitting ~ or + / - keys will toggle-collapse the entire thread you're on, so you don't have to hunt down the original poster's tiny minimize link.