It was an addon, but I think using CSS would be easier and preferable, and more customizable afterward.
Maybe some styles enxf.net/resources/categories/styles-2-x.8/ have the code already that I can use, but I'm not sure how to find one that does, since their titles are not descriptive. And most only seem to change the colors.
Also, this is really interesting and useful how we can reply in a threaded view. How did you do this? Is it an addon we can use on our own sites?