Hi, Please check if this happens in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. If the new profile is okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the needed personal data] from the old profile. Firefox stores your personal data and settings in [http://kb.mozillazine.org/Profile_folder another location (profile folder)] separate from its [http://kb.mozillazine.org/Installation_directory files/folder]. A new profile would have the default Firefox settings in ('''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Options%20window '''Options'''] and [http://kb.mozillazine.org/About:config about:config] ), and usually would also be empty of any '''Extensions''' and themes ('''Appearance''') in '''Tools''' > '''Add-ons''', and their settings. Also, a new profile would have no previous stored website cache/cookies/data/preferences etc., ('''Tools''' > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History '''Clear Recent History''']). [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files] [http://kb.mozillazine.org/About:config_entries about:config Entries]

Problem was maybe caused by Java having been disabled due to security vulnerability. Uninstalled Java, installed new version, restarted Firefox, enabled Java plugin, restarted again, and it seems to be working. Except that one site that I still can't do anything without getting immediately logged off.. but other sites seem to be ok so far, knock on wood? I don't know, I'll try a new profile next if problem recurs. I wish Firefox had a "repair corrupt profile" function instead of having to recreate and migrate like that.

Thanks for the helpful info.