GNU LibreJS, or simply LibreJS, is a free software web browser extension for Mozilla Firefox-based browsers, created by the GNU Project. Its purpose is to block nonfree nontrivial JavaScript programs and allow free or trivial JS in a user's web browser. The add-on was created to address the so-called "JavaScript Trap" described by Richard Stallman, a situation in which many users unknowingly run proprietary software in their web browsers.