Cool, I made one with the exact same principles to scratch a personal itch - inline reply is something I was hoping to add some time.

Anyway, I'd love to be able to just use someone else's extension :) Mine makes up/downvote and collapsing buttons easier to hit on mobile, links to parent/root comments, and rewrites Google AMP links to regular links. It's open source, so feel free to incorporate those features in yours: https://gitlab.com/vincenttunru/sihn