up down on instagram.com

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://www.instagram.com/*
// @require      http://code.jquery.com/jquery-latest.js
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    function getTop() {
        var winTop = $(window).scrollTop();
        var divs = $('article');
        var top = divs.filter(function(_, item) {
            return $(item).position().top <= winTop;
        });
        return top;
    }
    $(document).keypress(function(e) {
      if (e.charCode == 106) {
        getTop().last().next()[0].scrollIntoView();
      } else if (e.charCode == 107) {
        getTop().last().prev()[0].scrollIntoView();
      }
    });
})();