I found a clickjacking (UI redress) on opera.com!

While clickjacking is an effective attack in cases where only clicking or minimal key presses are required to perform a harmful action, typically in the context of a logged-in user’s account, we are not aware of any part of our site where a clickjack attack could have any significantly harmful consequences. We are aware that the site does not use clickjacking protection, but we are not able to see how a malicious attacker could use it against any parts of this site. (Parts of our other websites that need clickjacking protection will already use the header to prevent it. We only use the header on pages that actually need it.)

Therefore, we do not consider this to be an exploitable security issue, or even a bug. The lack of the X-Frame-Options header is intentional.