You will need to install a user script manager extension to install this script.
This script should not be not be installed directly. It is a library for other scripts to include with the meta directive
// @require https://greasyfork.org/scripts/456228-absolute-visibility/code/Absolute%20Visibility.js?version=1125944
Based on https://addons.mozilla.org/en-US/firefox/addon/always-visible/ and turned into a library that can be used on other UserScripts to disable visible state changes in websites.