Tampermonkey ( Greasemonkey ) for Android, Chrome, Chromium, Firefox, Edge, Opera, Safari.
http://openuserjs.org/about/Userscript-Beginners-HOWTO
http://openuserjs.org/about/Tampermonkey-for-Chromium
http://browser.yandex.com/tablet/ (Tampermonkey-for-Tablet)