Opera before 11.65 does not properly restrict the opening of a pop-up window in response to the first click of a double-click action, which makes it easier for user-assisted remote attackers to conduct cross-site scripting (XSS) attacks or execute arbitrary code via a crafted web site.
http://www.opera.com/support/kb/view/1020/
http://www.opera.com/docs/changelogs/windows/1200/
http://www.opera.com/docs/changelogs/unix/1200/