iframes of maps not interactive in firefox / embedded osm-css and -js don't load?

Hello everybody,

this is my first question here. I use iframes to embed osms in my webpage. It works fine in Chrome, but not in Firefox, were it used to work in the past.

The maps do show, but are not interactive anymore: Links are not clickable, the zoom-buttons are inactive, etc.

Apparently, Firefox does not load the css-file and the js-file that come with the embed.html that gets loaded via the iframe, since that portions shows in grey upon inspection of the embedded iframe on my webpage. How do I fix this?

I tried loading the css and the js in the header/body/after the body of my index.html instead, tried to fiddle with Firefox-settings concerned with security and also tried to use object instead of iframe, but to no avail.

Here is the code I use in HTML to embed the iframe:

<iframe width="xxx" height="xxx" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" style="border=none;" src="https://www.openstreetmap.org/export/embed.html?bbox=xxx"></iframe>

Thank you!