This is great! Not only does it toggle collapse state of comments, it also helps me quickly pinpoint how many layers deep I am within a thread. Unlike similar extensions, this one produces a thicker highlighted bar - which improves clarity substantially. Nice job, dev!

update (01feb2019): I should point out that I'm also using "Old Reddit Redirect" (extension that redirects me to the older design: old.reddit.com). Worth mentioning because this extension's last update was Jul 21, 2017. Working great on the classic design! Untested on whatever trendy new design reddit is fudging around with.