I got tired of refreshing a long thread to see that there were new comments (e.g. it went from 47 -> 52 comments) but then having to wade through and skim the whole thread again just to find them.

So I hacked this Tampermonkey/Greasemonkey script together that highlights them for me. Maybe you would find it useful. (Or make it better, I can do damage but I'm no js developer.)

https://gist.github.com/infogulch/77bcd65ae8dc0a3de9a99b00f9987732