Reddit broke for me on Firefox whenever they moved to ssl permanently, hitting the back button always reloads the page rather then going back to the cached state it was in so comments show uncollapsed. HN doesn't seem to have this problem.
I've noticed that too, is it only a Firefox thing? It's very annoying.
I think it is a reddit thing. I’m pretty sure I observed the same behavior when I used chrome (thought this was almost a year ago) and this still happens on my iPad using safari.