Double Click a ListBox item to open a browser

You can add a style to ListBox.ItemContainerStyle, and add an EventSetter there:

<ListBox>
    ....
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}" BasedOn="{StaticResource {x:Type ListBoxItem}}">
            <EventSetter Event="MouseDoubleClick" Handler="ListBoxItem_MouseDoubleClick"/>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

ListBoxItem_MouseDoubleClick is a method in your code behind with the correct signature for MouseDoubleClick.

I wanted to solve this without needing to handle the listBoxItem double click event in the code-behind, and I didn't want to have to override the listBoxItem style (or define the style to override in the first place). I wanted to just fire a command when the listBox was doubleclicked.

I created an attached property like so (the code is very specific, but you can generalise it as required):

public class ControlItemDoubleClick : DependencyObject {
public ControlItemDoubleClick()
{

}

public static readonly DependencyProperty ItemsDoubleClickProperty =
    DependencyProperty.RegisterAttached("ItemsDoubleClick",
    typeof(bool), typeof(Binding));

public static void SetItemsDoubleClick(ItemsControl element, bool value)
{
    element.SetValue(ItemsDoubleClickProperty, value);

    if (value)
    {
        element.PreviewMouseDoubleClick += new MouseButtonEventHandler(element_PreviewMouseDoubleClick);
    }
}

static void element_PreviewMouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    ItemsControl control = sender as ItemsControl;

    foreach (InputBinding b in control.InputBindings)
    {
        if (!(b is MouseBinding))
        {
            continue;
        }

        if (b.Gesture != null
            && b.Gesture is MouseGesture
            && ((MouseGesture)b.Gesture).MouseAction == MouseAction.LeftDoubleClick
            && b.Command.CanExecute(null))
        {
            b.Command.Execute(null);
            e.Handled = true;
        }
    }
}

public static bool GetItemsDoubleClick(ItemsControl element)
{
    return (bool)element.GetValue(ItemsDoubleClickProperty);
}

}

I then declare my ListBox with the attached property and my target command:

<ListBox ItemsSource="{Binding SomeItems}"
     myStuff:ControlItemDoubleClick.ItemsDoubleClick="true">
<ListBox.InputBindings>
    <MouseBinding MouseAction="LeftDoubleClick" Command="MyCommand"/>
</ListBox.InputBindings>
</ListBox>

Hope this helps.