Just to confirm, could you go back to the Options page, Privacy & Security panel, and check two things:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the left column, click Privacy & Security. Then on the right side:

• Make sure you have a checkmark next to "Remember logins and passwords for websites"

• Click the Saved Logins button and see what is listed there -- is it empty?

The above assumes that you were having Firefox save your logins rather than an add-on like LastPass or RoboForm.

Naturally an update should not erase your logins. It's possible that the old logins filed was sidelined but still available, or that we might be able to guide you toward a copy.

Do you make any backups of your Firefox data, for example, as part of a more general backup of your system?

Did Firefox perform a Refresh? The tell-tale sign, unless it was interrupted mid-stream, is a folder on your desktop named Old Firefox Data. If you see that folder, check inside to see how recent its contents are.

What about the rest of your profile? Settings, history, bookmarks . . . . .

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

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

In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.