If you are using the widget within a scrolling panel, with fixed width and height, you may have trouble with the position of the popup address list. We have a solution which involves wrapping the address input element in a div. You then pass that div as a parameter to the Addressfinder widget's constructor.
See the container option on the widget documentation page. We also have an example of its use here under ‘use with a scrolling panel’ on the code demos page.