This document explains how to enable and disable Opera's popup blocker. For general information on popup blockers, see Popup Blocker - FAQ.
Open Opera, click the Menu (Red "O" in the top left) and click Settings.
Expand the Advanced Menu and select Privacy & security.
Locate and select Content settings.
Scroll and select Pop-ups and redirects.
Toggle the Allowed button as desired. You can also black-list or white-list specific websites by clicking Add under Block or Allow.