OK, going by memory here, so please forgive me if the instructions aren't exact...
Look for the Tools menu; on that menu, look for Options; that should bring up a page which includes options for deleting files, cookies, etc.
I'm pretty sure, anyway.
Be careful, because it may delete *all* of your cookies, not just the one for FR.
You're right, there's a delete cookies there. Also one in the windows file. I wonder if that means that you have to delete the "login cookie" to actually log off. I'll try it anyway and see. Won't be too much of a tragedy if I delete them all, they come back, I think, when the site is revisited.
Thanks much, guys, for the help.