Found a Fix! I think...
For those of us that can log in with Internet Explorer, this should work, it did for me. Now, I wanted to make sure this would work, so I went--Tools---Options---"Clear All". (Please note that you will lose all saved passwords, cookies, history, ect...)
I then made a backup of my Bookmarks, as they are more up to date than IE's. Close Firefox and then reopen it. Select--File---Import---Next. Select which aspects to import, mainly "Cookies", but I selected everything but "Favorites". Close then reopen Firefox. You should now be able to login to the forums.
Important: Although you may not have to "Clear All" (maybe just clearing the cookies would work) I wanted to be sure. You could try just clearing and importing the cookies first.
I hope this is helpful.