Came across this as well [0]→[1].
(Slightly modernized version could be:)
javascript:void([].forEach.call(document.querySelectorAll('body *'),e=>/fixed|sticky/.test(getComputedStyle(e).position)&&e.parentNode.removeChild(e)))
[0] https://news.ycombinator.com/item?id=16516126
[1] https://alisdair.mcdiarmid.org/kill-sticky-headers/