This new feature in google called google instant preview (where you click the magnifying glass) that shows a snapshot of the page doesn't produce any ajax request or such as far as firebug can see. How is that possible? Is there another magic way of retrieving content without using an XMLHttpRequest (ActiveX for for the slow people)
The robot which collects the page has a "Google Web Preview" user agent. You could serve a version which doesn't show the popup when that user agent visits.