If you are a site owner, ensure your Content Security Policy is up to date to handle modern frame-ancestors requirements.

If you need to communicate between a parent and a child frame, use the window.postMessage API. It is the secure, modern standard.

ViewerFrame (often associated with specific legacy browser modes or internal frame-handling protocols) allowed developers—and sometimes attackers—to manipulate how a page refreshed or loaded content within a frame.

The primary reason for the patch was . Modern browsers (Chrome, Firefox, Safari) have moved toward a model where every site is isolated into its own process. The "ViewerFrame Mode" created a loophole where cross-origin data could potentially leak during the refresh state.