I wrote a JS bookmark that lets me jump to the next top-level comment on HN. I use it for finding interesting conversions without having to scroll and look for the next top-level comment.

It works by finding all of the comments with indent=="0". Then, each time the bookmark is clicked, it creates and follows a link. Each comment has a unique id so I just have to concatenate current_url + "#" + unique_id and follow that link.

Once the script reaches the bottom, it follows the "more comments" link and repeats the same process.

I plan to write something similar for Reddit