This function is called when links are dropped to the browser element, with the following arguments.

droppedLinkHandler(event, uri, name) -- Firefox 51 or older
droppedLinkHandler(event, links) -- Firefox 52 or newer

• event -- drop event, or null if no event is available
• uri -- uri string of the dropped link
• name -- name string of the dropped link
• links -- array of the dropped items with nsIDroppedLinkItem interface