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.
display: block !important;
Thanks, Sandy - this is super helpful. Has Marketo tried to hire you yet!?
Thanks for reporting this. I'm having engineering take a look right now.
We have a patch prepared for this which should be going live in the next few days.