You have to scroll faster than the combination of bandwidth size and JS computation. Turn it into a game: visit the site progressively working backwards through your old phones until you can 'win'.
Then see if you've got time to take a screenshot.
If you actually need to click a link in the footer the only way to win is not to play.
Even better: automatic infinite scrolling. Wanna click on something in the footer, where useful contact details can typically be found? Ooops too late, it's gone!
"No, we won't actually load the text at the bottom of the scollbar until you scroll down to it--and we'll only load it in a dribble." @#$%^&*()_+!