Could you try again in a new profile and only copy the logins.json and key3.db files?

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

atsoukias said

Got a new laptop. Copied contents of the old profile to the new profile. Most old information is there (bookmarks), but I do not see the passwords. I repeated the copying of the two files key3.db and logins.json specifically, but still the passwords saved on my old profile are not there ...

Thanks for the suggestion. It worked. Apparently the file causing the problem was the cert8.db containing the security certificates.