How to specify type for generic class?

Question

I found some code online that allows me to find controls of a specific type recursively within a Control in ASP.NET Web Forms. It works great. Here's the code:

internal class ControlFinder<T> where T : Control

    {

        private readonly List<T> _foundControls = new List<T>();

        public List<T> FoundControls

        {

            get { return _foundControls; }

        }

        public List<T> FindControls(Control control)

        {

            foreach (Control childControl in control.Controls)

            {

                if (childControl.GetType() == typeof(T))

                    _foundControls.Add((T)childControl);

                else

                    FindControls(childControl);

            }

            return FoundControls;

        }

    }

It can be consumed like this:

var textboxes = new ControlFinder<TextBox>().FindControls(control);

This is exactly what I needed, but I found a need to be more fluid, and allow passing in the type rather than just using "TextBox". In my case, if the input controls needed to be disabled, I have this method:

public static void DisableTextBoxes(this Control control)

        {

            var controls = new ControlFinder<TextBox>().FindControls(control);

            foreach (var textbox in controls)

            {

                textbox.Text = "";

                textbox.Enabled = false;

            }

        }

As I said, this works great. But I'd like to write an extension method that allows passing in the type when called. The relevant code would be changed to this:

public static void DisableTextBoxes(this Control control, Type type)

        {

            var controls = new ControlFinder<type>().FindControls(control);

Problem is, this doesn't work. I get an error stating that the type or namespace couldn't be found. Is it not possible to initialize a generic class with a variable?