Greasemonkey is a Mozilla Firefox extension that allows users to install scripts that make on-the-fly changes to web page content. Developed by Anthony Lieuallen, Aaron Boodman, Johan Sundström
License: Open Source
Greasemonkey is an open-source, lightweight extension primarily for Firefox, emphasizing privacy and user control, while Tampermonkey is a more feature-rich, cross-browser solution that offers a larger script repository and automatic updates. Both extensions allow users to customize web pages with user scripts, but Tampermonkey is generally more versatile and user-friendly.