const iframe = document.createElement("iframe");
    document.body.append(iframe);
    iframe.contentWindow...

    javascript:(function () {
        const rm = () => document.querySelectorAll('iframe')
            .forEach(f => f.remove());
        let timeout;
        const debouncedRm = () => {
            clearTimeout(timeout);
            timeout = setTimeout(rm, 100);
        };
        rm();
        new MutationObserver(debouncedRm)
            .observe(document.body, {
                childList: true, subtree: true
            });
    })();