Greasemonkey
A Firefox extension that runs user scripts to change how web pages look and behave.
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About Greasemonkey
Greasemonkey is the original userscript manager for Firefox. You install small JavaScript user scripts, and it runs them on matching pages to change layouts, add features or remove annoyances. It has a built-in script editor, automatic script updates and a GM.xmlHttpRequest API for scripts that need to fetch data from other sites.
Version 4.14, released in June 2026, adds a @match for the current page to new scripts, more editor options and clearer messages when automatic updates fail. It is available on Mozilla's add-on site.
Strengths
- Long-established userscript manager with a public bug tracker
- Built-in script editor
- Automatic script updates with failure reporting
- Still receiving releases in 2026
Limitations
- Firefox only
- Releases are infrequent
- Writing your own scripts requires JavaScript
Details
- Pricing
- FreeFree to install from Mozilla's add-on site.
- License
- Open source, license not stated
- Developer
- The Greasemonkey contributors
- Platforms
- Browser extension
- How it runs
- Browser extension
- Account
- Not required
- Best suited for
- Firefox users who want to run or write user scripts
- Categories
- Browser tools, Automation
- Last verified
- Added
- Provenance
- Facts checked against the developer's own pages and store listings, 1 sources on file.
Alternatives to Greasemonkey
Compare allSoftware that can replace Greasemonkey for an important use case, and what changes if you switch.
Tampermonkey
Userscript manager for running custom scripts on websites.
Tampermonkey runs the same scripts across every major browser rather than Firefox only, with backups and an editor, but it is closed source.
Violentmonkey
Open-source userscript manager with cloud backup.
Violentmonkey is open source under MIT, adds cloud backup of scripts through storage you own, and has slightly narrower compatibility than Tampermonkey for exotic scripts.
ScriptCat
A userscript manager extension compatible with Tampermonkey scripts that can also run background scripts.
ScriptCat is open source, runs Tampermonkey scripts and adds background scripts and extra APIs, though much of its script site community is Chinese-language.
Userscripts
An open-source userscript and userstyle manager for Safari on macOS and iOS.
Userscripts is an open-source manager for Safari on macOS and iOS that handles user styles too, and scripts from other managers may need adjustments.
Similar software
Related functionality, not necessarily a direct replacement.
