3
Not security--first thing I tried was lax security settings. Bear in mind I hadn't changed anything except for the extensions--firefox had been working fine with the site. Wasn't a cache issue either--kept clearing that. Turned firewall off so that wasn't it. The problem was shared by a few other firefox users who couldn't log on to mozzillazine (but all of us could log-on as usual with IE).
Here's how it went:
Firefox .92 worked fine.
Then I installed extensions--everything worked but log-in.
Deleted everything. (getting rid of extensions is a little bit of a pain until you learn how--the extension manager isn't very good at the uninstall part).
Firefox, fresh install worked fine.
Got bold and reinstalled extensions--couldn't login again.
Uninstall, delete, Firefox, fresh install--works fine.
So far haven't installed extensions to find out which one it was--frankly don't have time to mess it up again--would probably just go back to IE which I'd like to avoid.
Brian