trigger form onsubmit event if focus on dropdown

[John A Grandy]

For a <form method="get"> containing an <input type="text"> , a <select> ,
and an <input type="submit"> .......

I find that the form's onsubmit event is triggered by pressing enter if the
focus is on the textbox , but not if the focus is on the dropdown.

Does anyone know why this is and how to fire the onsubmit event on pressing
enter if the dropdown has the focus ?