Don't mark everything above the clicked-on post as read.
I read a lot of webcomics/time ordered content in and it is incredibly annoying that clicking on a post automatically marks everything above it (i.e. everything I'm about to read) as read. It means that I have no idea where I'm up to through a browser restart.
Please Please, never mark something as read if i've never actually opened and/or read it.
(Tested in Chrome/FF)
You might want to disable “Scrolling through posts marks them as read” in settings.