About Greasemonkey
Greasemonkey is where userscripts started. It is a free, open source manager for Firefox, licensed under MIT, and the other managers took their script format from it. Its Add-ons page describes it as a way to customise how a page displays or behaves using small bits of JavaScript.
It does the core job without a lot around it: install a script, edit it in the built-in editor, turn it on or off, and let it update itself. Recent releases added a @match line for the current page when you start a new script and better messages when automatic updates fail. It supports the GM.xmlHttpRequest function and other standard calls, and because it is Firefox only, there is no Allow User Scripts step to deal with.
Its limits are scope and pace. It runs on Firefox alone, the feature list is shorter than Tampermonkey's or Violentmonkey's, and development is slow, though the GitHub project received a version bump to 4.14 in June 2026. Some modern scripts use features it does not offer. The extension has about 157,000 Firefox users and a 4.2 rating from 1,293 reviews. It is a good, quiet fit if you use Firefox and want something small, but most people will be happier with Violentmonkey or Tampermonkey.
Pros and cons
- The original userscript manager, open source under MIT
- Simple and focused, with a built-in editor
- Still maintained, with version 4.14 in June 2026
- Free
- Firefox only
- Smaller feature set than Tampermonkey or Violentmonkey
- Slower development than the leaders
Permissions
It asks for access to all websites so scripts can run on any page, plus tabs, storage, cookies and downloads access that script functions rely on. Web request access supports cross-site requests made by scripts.
