Messages not marked as read

I have one of my forum users who keeps complaining that often times read messages will show up unread even after they've been read...multiple times even and sometimes he will visit and there will be a bunch of new posts that aren't flagged as read.   I think he is using Fire Fox, is this a compatibility issue?

I also have a member (not the same one) who is using IE8, and cannot see the chatango box.  she said there is just a gray square where it is supposed to be.  I know youguys do not control chatango, I am just curious to see if anyone else has had the same problem.