If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

What about the rest of your profile? Bookmarks, settings, toolbars?

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

You would need older backup copies of logins.json and key4.db to recover the lost passwords.

You can look at this utility to browse System Restore points.

• System Restore Explorer
  http://nicbedford.co.uk/software/systemrestoreexplorer/

Did you already reboot the computer?

You can also check for orphaned profiles that aren't listed in the Profile Manager and on the about:profiles page (profiles.ini).

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