Makes tabs and windows think they're visible even when they're not.
此脚本不应直接安装。它是供其他脚本使用的外部库，要使用该库请加入元指令 // @require https://update.cn-greasyfork.org/scripts/456228/1309113/Absolute%20Visibility.js
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.
