Can i have scrollable pop up when i click on IList property with Plus Sign in EDIT mode . 

Below is my code where i am clicking on Plus sign in IList property .After clicking on One pop up will be opened populated with Country List. But In this pop up Scrollable option is Not Showing Up.

Can Any one help me to say How i can show the  scrollable pop up with Cuntry List.

[Display(Name = "Restricted For", GroupName = SystemTabNames.PageHeader, Order = 5)]
[EditorDescriptor(EditorDescriptorType = typeof(CollectionEditorDescriptor))]
[Editable(true)]
public virtual IList CountryRestrictedFor
{
get;
set;

}

Thank In advance

--Sourav