// ==UserScript==
// @name       Twitter followers
// @include    https://twitter.com/*
// @version    0.1
// @author     sportclub2010
// @grant      none
// ==/UserScript==

if (document.location.href.indexOf('followers') != -1){
    var Grid = document.getElementsByClassName('Grid-cell u-size1of2 u-lg-size1of3 u-mb10');
    Array.from(Grid).filter(b => !b.querySelectorAll(".btn-group:not(.not-following)").length);

    var i=0;
    var btn = [];
    function Timer() {
        btn = Grid[i].getElementsByClassName('user-actions-follow-button js-follow-btn follow-button');
        if(btn[0]){
            btn[0].click();
        }
        i++;
        if(i<10) setTimeout(Timer, 2000);
        //if(i<Grid.length) setTimeout(Timer, 2000);
    }
    setTimeout(Timer, 2000);
}

// Тестирую например на этой странице https://twitter.com/slojno/followers