I have also another additional idea to make the importer module safer if you're comfortable with it

https://github.com/mozilla-b2g/gaia/blob/master/apps/communications/contacts/js/importer_ui.js#L781
Just after the user clicks on "Import button", we could call something like this:

```js
imgLoader.unload(); // or imgLoader.uninit() or imgLoader.destroy(),...
```

This method should remove the listeners "scroll" and "onupdate" thought. I guess that to keep listeners running does not make sense here.

What do you think @jmcanterafonseca ?