3 rows login
It seems that FF can only remember 2 rows or fields of login forms. When I fill a login form that has 3 or more fields FF only remembers and stores 2 fields. Looking at the stored user/password data (about-security-login) there are only 2 fields stored: username and passwords. what happens where a website wants 3 fields to be filled in? Is this cannot be stored by FF?
ప్రత్యుత్తరాలన్నీ (2)
No, Firefox can't deal with three fields. Websites can't "make up things" that don't meet W3C standards and expect all web browsers to "cater to their unique needs".
An example of websites where you need that might be helpful so that one of the support contributors here migh have a workable / usable suggestion for you.
Note that yu posted with an unofficial Waterfox 56.3 version, so you would need to contact Waterfox for support if you would want such a feature.
Firefox does come with recipes to deal with specific forms.
You can try a form fill extension to see if you can find one that works in this case.