Look on your desktop. Do you see a folder called; Old Firefox? Look inside. Look for the folder with the latest creation date.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar. How many profiles are listed? How many should be there? Also, open the profile folder in your file explorer.

Surely when Firefox updates we should either be warned to protect passwords and bookmarks or the Firefox people should have sufficient respect for those using Firefox not to repeatedly cause this problem. I'm 72, relative knowledgeable, but if FF can't solve what would appear to be a very simple problem for them to solve then, and I really don't want to, change browsers.

Really, really disappointing as I had to spend 3 hours recreating user/password links. We are told not to write down passwords but what other option is there?

Looked in Old Firefox data - last modified 10 Dec 2019 so not much point going there. Don't worry anymore I'm off to Brave.