Hidden Sites

Select View->Hidden Sites... from the main menu or click the corresponding button on the toolbar to activate the hidden sites dialog. All hidden sites are listed in this dialog. These sites may have been manually hidden by user, or have been automatically hidden by the popup killer. When the popup killer detects a popup window, it hides the site for a particular time and then closes it permanently. That time gives you opportunity to recover a useful popup window.

Show
You can select an item among all the listed sites and click <Show> button to make that site visible. You can use this button to recover a popup window before it's closed permanently. 
Add Into White List
Click <Add Into White List> button to add the selected site into the white list so that it will not be identified as popup ads again.