Duplicate works properly now but there is a delay before the duplicated tab is made active. Maybe instead of waiting for tabs.duplicate add a listener to tabs.onCreated and assume the next tab created is the duplicated one, make it active, then remove the listener.
I've now tried this and it is no faster at changing the focus. As the listener could in theory pickup on a created tab that wasn't made by the add on, I'm going to leave the add on as it is using .then()
