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.

Please bear with me -- I don't want to do more damage than I have already.

So, if I go to my external hard drive and copy the Firefox profile information from Sunday, then go to my Mac library, open the corresponding folder, and paste it there, I should be OK?

I do SO much better with phone support, because I can repeat the instructions back to them before I do anything.

Again, I appreciate your help and patience, Fred.

Yes. Remember to Copy the files.

Hey, FredMcD: I tried the backup method, but I still have nothing from my previous versions.

At this point, am I better off scheduling an appointment at an Apple Store and let them figure it out?

It just doesn't seem possible that this should be this difficult.

Thanking you in advance for any advice.

If that is what you want. Create a copy of the instructions here and give then to the tech.

I will do so. Sorry I'm so dense about this. I thank you for your help and kindness.