Hi EHSANRF, could you describe what changed on your Windows? Was there a major update, or Refresh, etc.?

jscher2000 said

Hi EHSANRF, could you describe what changed on your Windows? Was there a major update, or Refresh, etc.?

Hi, yes. I changed the motherboard and the SSD. My Windows always gets the latest updates. I desperately need information and passwords in my Firefox account.

Thank you for the additional information.

Locally stored data

When you changed the SSD, did you restore all the data from the previous drive? Firefox data is stored under the User profile path in AppData.

First, set Windows to show hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Next, explore up the path within your backup (or old drive, or wherever you restored the data):

\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles

Each individual profile folder would have its own data files. This article describes the most useful ones: Restore bookmarks, passwords, and data from an old Firefox profile.

Firefox Account Sync data

If you have allowed a couple hours for Firefox to Sync by now and you haven't recovered the missing data that way, I suspect it is not there.