Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

Look on your desktop. Do you see a folder called; Old Firefox?

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

usernames & passwords exist but are not shown in page info list

That information is kept in the Password Manager.

Password Manager in page info i knew

You can check in Windows Explorer if there is a previous version of the logins.json and key3.db files available.

• Right-click: Properties > Previous Versions
• http://windows.microsoft.com/en-us/windows-8/how-use-file-history

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox