Mysterious horizontal scroll on my friends computer, but not on mine

Hi All,
When I QC my site on my friends’ computer there’s a very small horizontal double scroll bar on the homepage. When viewed on FireFox


I don’t see on my laptop, both in the browser or the preview mode. All my sections have overflow off AND when I go to preview mode on his computer the horizontal scroll isn’t there either. I don’t understand how to fix something I can’t see.

Any help is much appreciated

browser version

Read only

Here is my site Read-Only: LINK
(how to share your site Read-Only link)