I believe this is a poor solution, because the problem is simply with web browser design. Website-initiated popups should remain inside the browser tab, and the browser tab should always be closable. There is NO excuse for a web browser to allow a website to, even temporarily, disable it's UI, particularly the UI to close it. Scripting that controls your browser should not be allowed. Nontechnical users need to be able to trust their browser UI. Message boxes that look like OS prompts should simply not be available options for websites to use.