Dom elements do not work with 1 variable and do not work with "let" variables

Question

✅ Works when creating 2 variables:

var val;

var list = document.querySelector('.list-group');

val = list;


val = list.childNodes;

console.log(val);

    <ul class="list-group">
        <li>1</li>
        <li>2</li>
    </ul>

❌ 1 variable does not work:

var list = document.querySelector('.list-group');


list.childNodes;

console.log(val); 

     <ul class="list-group">
        <li>1</li>
        <li>2</li>
    </ul>

❌ Doesn't work in firefox and chrome console with let variable:

let val;

let list = document.querySelector('.list-group');

val = list;


val = list.childNodes;

console.log(val);

    <ul class="list-group">
        <li>1</li>
        <li>2</li>
    </ul>

works with the same operations on Udemy video and StackOverflow

What are the differences between? Why firefox does not work with the let variable?