I just tried, and I can only use my adblocker to block the element that requests I login. My scrolling is still stopped, and I can't see anymore of a user's photos. Am I missing something?
I use all of uBlock origin's annoyance filters and it works for me.
www.instagram.com##body:style(overflow-y:auto!important; max-height:none!important; width:auto!important; position:static!important;)If you permablock it with the picker the scroller will break. They have something from the modal logic tied into the scrolling logic.