Userscript manager
A userscript manager is a type of browser extension and augmented browsing technology that allows users to install scripts (written in JavaScript) to modify webpages as they browse them, and provides an interface to load, create, and organize userscripts. Userscripts are often referred to as Greasemonkey scripts, named after the original userscript manager Greasemonkey for the Firefox browser. Several host sites make repositories available for sharing scripts.