The Pop-up Blocker Settings window should now be visible, overlaying your browser window. The first section in this window, labeled Exceptions, allows you to specify certain sites on which you wish to allow pop-ups to appear.
At the top of this section is an entry field labeled Address of website to allow:. Enter the URL of the site on which you would like to allow pop-ups here. In the example below, www.about.com was entered. Next, click on the Add button located to the right of this field. After clicking Add, you will notice that the site you entered is now displayed in the Allowed Sites list.