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// ==UserScript==
// @name        FF Reader Mode Wide
// @namespace   finchd
// @description Make Reader Mode 90% instead of fixed-width
// @include     about:reader?*
// @version     1.1
// @grant       none
// ==/UserScript==

if (document.getElementById('container')) {
  var s = document.createElement('style');
  s.type = "text/css";
  s.innerHTML = ".container {" +
      "max-width:90% !important;"
    "}";
  (document.head || document.documentElement).appendChild(s);
}