Cookie problem of some kind. My work computer was automatically updated to the latest version of Firefox. My home computer (a Mac) was not yet updated. I still had the problem at home, but updating Firefox and deleting all the associated cookies seems to have fixed the problem so far. I will try a more thorough cookie deletion tomorrow at work and see if that fixes it.

Note I seem to have had a few problems at other sites as well at ho,e, same process seems to have worked OK.