Something, like this:
var height = document.documentElement.scrollHeight;
var width = document.documentElement.scrollWidth;
function scroll(event){
var y = event.clientY;
var yPercentage = y/screen.height;
var x = event.clientX;
var xPercentage = x/screen.width;
//ctrlKey is subject to change as more features will be added
if (event.ctrlKey)
window.scrollTo(xPercentage*width,yPercentage*height);
}

window.onmousemove = scroll;
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In addition I found, that this addon does not work on addons.mozilla.org (on mozilla.org it works)