I am trying to compare scrolling behavior on a mobile vs desktop website. The plan is to let participants scroll on a mobile phone and desktop in a lab respectively for x minutes. Therefore, I have full control over the devices. How do I capture the scrolling events on third-party websites such as Reddit? Google Chrome has a feature called performance insights to track user behavior, but it does not record scrolling. What are some viable alternatives to record the scrolling of users on mobile and desktop?
I think the simplest way is to create a bookmarklet that injects a tracking script into the website you want to track.