addons.mozilla.org
FireMonkey is a Firefox browser extension that functions as a lightweight combined user script and user style manager. It provides similar functionality to user script managers such as GreaseMonkey, Tampermonkey and Violentmonkey, and user CSS managers such as Stylish, Stylus and xStyle. It supports GM3 and GM4 script functions, allows users to toggle scripts and CSS on or off via a toolbar button, contains no tracking or advertising, and is released under the Mozilla Open Source licence. It has experimental support for Firefox for Android.
