Sorry for triple posting, but just wanted to test this out real quick. The script seems to basically work, but I've found a couple issues; After my second post it showed the line only on the first post. The second post didn't get a collapse line until I collapsed/uncollapsed the first post.
Second, when I edited a comment it removed the collapse line from that post until I edited a second time. This doesn't seem to be consistent.
Third, and this might just be on my end, at some point while editing the posts, the second post is now on the far right of the comments window, instead of just slightly to the right of its parent comment.
I don't think these issues will be a huge deal, and I'm still looking forward to using this. Thanks for making it!
EDIT: Should also mention I'm on Firefox as well, incase that matters.