KDE Native apps stores passwords different from Firefox, these are those differences:

Inside KWallet there is a folder called Form Data, it stores passwords used in forms, the Map subfolder contains one (and only one) entry for each form of each web page, the format of the hash is:

url#form_name

for example:

http://www.somedomain.com/somefolder/somepage.html#login

Inside this entry, there is one key with the name of the username entry and one key for the password entry of the referenced form, each of them containing the stored username and the stored password. For example:

http://www.somedomain.com/somefolder/somepage.html#login
secret_user -> user1
secret_password -> somepassword

You can not store more than one username/password pair for each form, if you try to use another username/password combination, the old entry is replaced with the new one.

Passwords for entire web pages are stored in a folder inside kwallet called Passwords. The Maps subfodler contains one (and only one) entry for each site, the format of the hash is:

protocol-hostname[-servicename]

for example:

http-localhost:631-CUPS

or

https-mail.somecompani.com:-1-Zimbra

Inside each entry, there is a combination of entries with the format:

https-mail.somecompani.com:-1-Zimbra
login -> username1
password -> password1
login-2 -> username2
password-2 -> password2
login-3 -> username3
password-3 -> password3


Inside the Firefox extension I would need to access DOM in order get the form data (form name, username, username field, password, password field), and match it to the information inside kwallet. I would still need a secondary folder to store additional form users, and not just one. And the way konqueror stores its forms passwords, you can not distinguish wich is the username and wich is the password, here again I would need to access DOM.
In order to use the Passwords folder I would need to access the URL of the page.
Firefox does not use the url to store passwords, it just uses the full host name. I would have to get the URL from the page in order to store it with the other info.
There is a tool for passwords administration, inside this tool, there is no DOM, so it is imposible to distinguish passwords from usernames in this tool.