Were the logins and passwords deleted from Firefox or is this a Firefox Lockwise issue? The easiest way to check is to do the following:

1. Go to the about:config page in Firefox to open the Configuration Editor for Firefox.
2. Bypass the security warning (we'll be careful).
3. Find the signon.management.overrideURI preference.
4. Erase it's value.

Now, you should be able to use the legacy password manager. See if you can view the logins and passwords in there. If you can, it's an issue exclusively with Firefox Lockwise.

Once you've checked, repeat the steps above, but reset the signon.management.overrideURI preference back to it's default value.

If you can see the passwords in the old legacy password manager, the issue is obviously related to Firefox Lockwise. Something that's caused some people problems is that Firefox Lockwise (and some other Firefox features) won't work properly if you have disabled e10s on Firefox.

If you have disabled e10s, you will need to enable it again in order for Firefox Lockwise to display the logins and passwords.

Hope this helps.

Thank you for your answer.

In the meanwhile I figure out that the logins.json file was corrupted, probably because my laptop shut off when the battery was empty. Fortunately I had a back up, after replacing the logins.json file, now I can see again all my logins.

Glad to hear that you got it sorted!

That can be a common issue with some internet security or antivirus programs. There are other reason that this might happen as well. Fortunately, you were able to recover everything.