Bookmarklet to Autoscroll Webpages (with commands); sped up-- also works on facebook now.

auto_scroll_bookmarklet.js

javascript: (function() {
    var a = document.body.clientHeight
    var b = document.documentElement.scrollHeight
    var c = document.documentElement.clientHeight
    var d = innerHeight
    var e = document.height

    console.log("document.body.clientHeight:\t\t\t\t\t" + a + ";\ndocument.documentElement.scrollHeight:\t\t" + b + ";\ndocument.documentElement.clientHeight:\t\t" + c + ";\ninnerHeight:\t\t\t\t\t\t\t\t" + d + ";\ndocument.height:\t\t\t\t\t\t\t" + e);

    if (document.URL.includes("facebook.com")) {
        (function() {
            var intervalObj = null;
            var retry = 0;
            var clickHandler = function() {
                console.log("Clicked; stopping autoscroll");
                clearInterval(intervalObj);
                document.body.removeEventListener("click", clickHandler);
            }

            function scrollDown() {
                var scrollHeight = document.body.scrollHeight,
                    scrollTop = document.body.scrollTop,
                    innerHeight = window.innerHeight,
                    difference = (scrollHeight - scrollTop) - innerHeight

                if (difference > 0) {
                    window.scrollBy(0, difference);
                    if (retry > 0) {
                        retry = 0;
                    }
                    console.log("scrolling down more");
                } else {
                    if (retry >= 3) {
                        console.log("reached bottom of page; stopping");
                        clearInterval(intervalObj);
                        document.body.removeEventListener("click", clickHandler);
                    } else {
                        console.log("[apparenty] hit bottom of page; retrying: " + (retry + 1));
                        retry++;
                    }
                }
            }

            document.body.addEventListener("click", clickHandler);

            intervalObj = setInterval(scrollDown, 1000);

        })()
    } else {
        let _ss_interval_pointer;
        let _ss_speed = 1;
        let _ss_speed_pairs = [
            [0, 0],
            [25, 200.0],
            [36, 120.0],
            [49, 72.0],
            [64, 43.2],
            [81, 25.9],
            [100, 31.0],
            [121, 37.2],
            [144, 44.8],
            [169, 26.4],
            [196, 32.0]
        ];
        let _ss_last_onkeypress = document.onkeypress;
        _ss_stop = function() {
            clearTimeout(_ss_interval_pointer)
        };
        _ss_start = function() {
            _ss_abs_speed = Math.abs(_ss_speed);
            _ss_direction = _ss_speed / _ss_abs_speed;
            _ss_speed_pair = _ss_speed_pairs[_ss_abs_speed];
            //_ss_interval_pointer = setInterval('scrollBy(0,' + _ss_direction * _ss_speed_pair[0] + '); if((pageYOffset<=1)||(pageYOffset==document.height-innerHeight)) _ss_speed=0;', _ss_speed_pair[1]);
            _ss_interval_pointer = setInterval('scrollBy(0,' + _ss_direction * _ss_speed_pair[0] + '); if((pageYOffset<=1)||(pageYOffset==document.documentElement.scrollHeight-innerHeight)) _ss_speed=0;', _ss_speed_pair[1]);
        };
        _ss_adj = function(q) {
            _ss_speed += q;
            if (Math.abs(_ss_speed) >= _ss_speed_pairs.length) _ss_speed = (_ss_speed_pairs.length - 1) * (_ss_speed / Math.abs(_ss_speed))
        };
        _ss_quit = function() {
            _ss_stop();
            document.onkeypress = _ss_last_onkeypress;
        };
        document.onkeypress = function(e) {
            if ((e.charCode == 113) || (e.keyCode == 27)) {
                _ss_quit();
                return;
            };
            if (e.charCode >= 48 && e.charCode <= 57) _ss_speed = e.charCode - 48;
            else switch (e.charCode) {
                case 95:
                    _ss_adj(-2);
                case 45:
                    _ss_adj(-1);
                    break;
                case 43:
                    _ss_adj(2);
                case 61:
                    _ss_adj(1);
                    break;
            };
            _ss_stop();
            _ss_start();
        };
        _ss_stop();
        _ss_start();
    };


    /*
    0-9 : Set scroll speed, 0 being stand-still and 9 being skim-speed
    –   :   Decrease speed
    =   :   Increase speed
    q   :   Quit

    Credit: http://tim.theenchanter.com/2008/08/autoscroll-in-safari-firefox.html
    */
})()

//below is the same script except in bookmarklet form
/*
javascript:(function(){var a=document.body.clientHeight,b=document.documentElement.scrollHeight,c=document.documentElement.clientHeight,d=innerHeight,e=document.height;if(console.log("document.body.clientHeight:\t\t\t\t\t"+a+";\ndocument.documentElement.scrollHeight:\t\t"+b+";\ndocument.documentElement.clientHeight:\t\t"+c+";\ninnerHeight:\t\t\t\t\t\t\t\t"+d+";\ndocument.height:\t\t\t\t\t\t\t"+e),document.URL.includes("facebook.com"))!function(){var e=null,t=0,s=function(){console.log("Clicked; stopping autoscroll"),clearInterval(e),document.body.removeEventListener("click",s)};document.body.addEventListener("click",s),e=setInterval(function(){var o=document.body.scrollHeight-document.body.scrollTop-window.innerHeight;o>0?(window.scrollBy(0,o),t>0&&(t=0),console.log("scrolling down more")):t>=3?(console.log("reached bottom of page; stopping"),clearInterval(e),document.body.removeEventListener("click",s)):(console.log("[apparenty] hit bottom of page; retrying: "+(t+1)),t++)},1e3)}();else{let e,t=1,s=[[0,0],[25,200],[36,120],[49,72],[64,43.2],[81,25.9],[100,31],[121,37.2],[144,44.8],[169,26.4],[196,32]],o=document.onkeypress;_ss_stop=function(){clearTimeout(e)},_ss_start=function(){_ss_abs_speed=Math.abs(t),_ss_direction=t/_ss_abs_speed,_ss_speed_pair=s[_ss_abs_speed],e=setInterval("scrollBy(0,"+_ss_direction*_ss_speed_pair[0]+"); if((pageYOffset<=1)||(pageYOffset==document.documentElement.scrollHeight-innerHeight)) _ss_speed=0;",_ss_speed_pair[1])},_ss_adj=function(e){t+=e,Math.abs(t)>=s.length&&(t=(s.length-1)*(t/Math.abs(t)))},_ss_quit=function(){_ss_stop(),document.onkeypress=o},document.onkeypress=function(e){if(113!=e.charCode&&27!=e.keyCode){if(e.charCode>=48&&e.charCode<=57)t=e.charCode-48;else switch(e.charCode){case 95:_ss_adj(-2);case 45:_ss_adj(-1);break;case 43:_ss_adj(2);case 61:_ss_adj(1)}_ss_stop(),_ss_start()}else _ss_quit()},_ss_stop(),_ss_start()}})()
*/