Extension method for List AddToFront(T object) how to?

List<T> already has an Insert method that accepts the index you wish to insert the object. In this case, it is 0. Do you really intend to reinvent that wheel?

If you did, you’d do it like this

public static class MyExtensions 
{
    public static void AddToFront<T>(this List<T> list, T item)
    {
         // omits validation, etc.
         list.Insert(0, item);
    }
}

// elsewhere

List<int> list = new List<int>();
list.Add(2);
list.AddToFront(1);
// list is now 1, 2

But again, you’re not gaining anything you do not already have.