There is actually a HNES[0] with both firefox[1] and chrome[2] support. I use it primarily because it highlights new comments from the last time I visited a submission.

[0] https://github.com/etcet/HNES

[1] https://addons.mozilla.org/en-US/firefox/addon/hnes/

[2] https://chrome.google.com/webstore/detail/bappiabcodbpphnojd...