I think you mean the Network settings in Windows. This isn't manged by Firefox, and has nothing to do with your passwords. Firefox's password manager has separate preferences Password manager - Remember, delete and change saved passwords in Firefox

If you have clicked to Never remember the password then you have created a block exception.

You can inspect and manage permissions for the domain in the currently selected tab via these steps:

• Click the "Site Identity Button" (globe/padlock) on the location/address bar
• Click "More Information" to open "Tools > Page Info" with the Security tab selected
• Go to the Permissions tab (Tools > Page Info > Permissions) to check the permissions for the domain in the currently selected tab

You can inspect and manage permissions for all domains on the about:permissions page.

• https://support.mozilla.org/kb/how-do-i-manage-website-permissions

If this is a choice made on a web page then this choice is likely stored in a cookie or possibly in local DOM storage. In such a case you can try to remove the cookies or possibly use "Forget About This Site".

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data like a bookmark from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.