Marked as read in Firefox

[Rotus8]

Threads that have been read don't seem to be noted in FireFox for me. Using Forum Tools > Mark as Read works. If I read a thread, then go back and refresh, it is still not marked. IE seems better at it. It used to work. Do I have a configuration issue or something? I checked and I have the latest versions of FireFox and Java.

Thanks for any help.