Add find.4chan search bar to the bottom of every thread

// ==UserScript==
// @name     Add find.4chan search to every thread
// @version  1.0
// @include  http*://boards.4chan.org/*
// @include  http*://boards.4channel.org/*
// @grant    GM_addStyle
// ==/UserScript==
document.getElementById("boardNavDesktopFoot").innerHTML += '<div id="search" style="float:right;display:inline;"> ' +
    '<form id="searchForm" target="_blank" action="https://find.4chan.org"> ' +
      '<input type="checkbox" id="nsfwBox" title="Search NSFW?" CHECKED> ' +
    '<input name="q" id="searchBox" type="text" value="" placeholder="Search 4chan!" /> ' +
    '<input type="submit" value="Search" /> ' +
    '</form> ' +
    '</div> ';

var checkBox = document.getElementById("nsfwBox");
checkBox.addEventListener('change', function() {
  if (this.checked) {
    document.getElementById("searchForm").setAttribute("action", "https://find.4chan.org");
    document.getElementById("searchBox").setAttribute("placeholder", "Search 4chan!");
  } else {
    document.getElementById("searchForm").setAttribute("action", "https://find.4channel.org");
    document.getElementById("searchBox").setAttribute("placeholder", "Search 4channel!");
  }
});