Warning! On the near horizon is a version of Firefox that will break embedded forms. As I noted in Firefox Developer Edition, Firefox 46 -- already in-the-wild for folks using Firefox Developer Edition -- is moving into Beta on March 8 and will be released worldwide via auto-update on April 19.
Luckily, your faithful forms guy has a fix you can put in place now to avoid disruption. Add the following style either in a <style> tag or via an external stylesheet. If you use an external stylesheet, make sure it loads before forms2.js/forms2.min.js.
#MktoForms2XDIframe {
visibility: hidden;
position: absolute;
display: block !important;
}
Maybe the offer got caught as spam.