Dismissing an add-on closes the process window

[mitchelljkotler]

Dismissing an add-on closes the processing window, which makes dismissing multiple add-on runs tedious. This is low priority.

[allanlasser]

I've narrowed down this issue to our Dropdown component's closeOnEventOutside handler. The dropdown is closing because the dismiss button fails a check for dropdown.contains(event.target). I'm not sure why this is happening, as the button is definitely in the dropdown node's tree.