<form style="border:1px solid #ccc;padding:3px;text-align:center;" action="https://feedburner.google.com/fb/a/mailverify" method="post" target="popupwindow" onsubmit="window.open('https://feedburner.google.com/fb/a/mailverify?uri=123456', 'popupwindow', 'scrollbars=yes,width=550,height=520');return true"><p>Enter your email address:</p><p><input type="text" style="width:140px" name="email"/></p><input type="hidden" value="123456" name="uri"/><input type="hidden" name="loc" value="ru_RU"/><input type="submit" value="Subscribe" /><p>Delivered by <a href="https://feedburner.google.com" target="_blank">FeedBurner</a></p></form>

<form style="border:1px solid #ccc;padding:3px;text-align:center;" method="post" action="https://www.feedburner.com/fb/a/emailverifySubmit?feedId=123456" onsubmit="window.open('https://www.feedburner.com/fb/a/emailverifySubmit?feedId=123456&amp;email=' + encodeURI(document.getElementById('feedburner-sub-email').value), 'feedburner-sub-window', 'scrollbars=yes,width=550,height=520'); return false;">
<p>Введите почтовый адрес:</p>
<p><input type="text" style="width:140px" name="email" id="feedburner-sub-email" /></p>
<p><input type="hidden" value="https://feeds.feedburner.com/~e?ffid=123456" name="url" />
<input type="hidden" value="ИМЯ ВАШЕГО ФИДА" name="title" />
<input type="hidden" name="loc" value="ru_RU" />
<input type="submit" value="Подписаться" /></p>
<p>Поставляется <a href="https://feedburner.google.com"  onclick="window.open(this.href);return false;">FeedBurner</a>
</form>