I can't even read. You say you ARE closing and restarting your browser. I have a different answer for this- don't close the browser! Car-seat.org is different than most other boards I've used, in that with this one I've discovered that I can actually change computers and if it's within an hour (the timeout for having been "logged in"), it will pretend that I haven't been there since the same "last time" as the computer I left.
Clear as mud.
Ok, so for example, right now it says "You last visited: Today at 01:53 AM". I can read and poke around, and things update, and everything is great. If I left and didn't do anything on the site for an hour, it would give my last visited as probably something like 10:04 AM (when I first came onto car-seat.org this morning), and "new posts" and "user cp" would show threads only since now (when I stopped loading anything on the site). BUT, if I switch computers and log back in as me, it'll say "You last visited: Today at 01:53 AM", and will show me everything new since 2AM (or so... whenever I loaded soemthing last in that 1:53AM session), just like it did this morning at 10AM on this computer. Same thing if I switch browsers, or if I quite Firefox and restart it.
WHY it does that, I don't know, but it's actually less annoying for me than other boards where if Firefox (or my computer) crashes or something, the board comes up empty (well, no new posts since last visit).