If you want to create a li
element for each input/name, then you have to create it, with document.createElement
[MDN].
Give the list the ID:
<ol id="demo"></ol>
and get a reference to it:
var list = document.getElementById('demo');
In your event handler, create a new list element with the input value as content and append to the list with Node.appendChild
[MDN]:
var firstname = document.getElementById('firstname').value;
var entry = document.createElement('li');
entry.appendChild(document.createTextNode(firstname));
list.appendChild(entry);