Video embedded from Youtube not displayed in Firefox and Explorer

Hello,

I have a problem with the visualization of a video embedded from youtube in a landing page using this marketo's guide (i need to track the video): developers.marketo.com/blog/send-view-data-from-a-youtube-video-to-marketo/

My problem is that at the beginning i saw the video in all the browsers (Chrome, Firefox and Explorer). Now i see the video only in Google Chrome.

Why this is possible? How i can fix this bug? There is another way to embedded the video so that it is responsive?

Thanks,

Gaspare