The immersive skin background will scroll along with the page after collapsing the Billboard in Firefox browser because of the site page css that was set for the html and body element.
I found out that there are CSS from the site page that is causing the issue. Here is the css that is causing the issue below:
overflow: auto; //<- this is inline css of the body.
Without the css above that was set by the publisher site content, the immersive skin background should be working fine.
- MDX 2.0
- Test page
- Apply CSS below to the specific site programmatic settings.