Sounds like it did a refresh.

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

Many thanks and very much appreciated, yes the is an Old Firefox folder on my desktop.

Thank you for pointing me in the right direction and giving me the links to guides I need. I will try to follow the instructions when I have a clear head. (I am not very techie and have low confidence, so need to build up to it.)

Big thanks FredMcD for very helpfully pointing me in the right direction.

Keep us posted.