How-to Detect Greasemonkey

02 Sep 2011

If you are a Greasemonkey user, then you may be surprised to know that Greasemonkey is informing every page that you visit that you are a Greasemonkey user.

Since Greasemonkey is a add-on that not every Firefox user has installed, that is personally identifiable information, and a potential security risk, so that is why Scriptish was made to be completely stealth.

Anyhow, if you are curious how to detect Greasemonkey as a webdev, well here’s how you do it:

Option 1

if (Components.interfaces.gmIGreasemonkeyService) {
  alert("I smell a monkey!");
}

Option 2

<script type="text/javascript" src="resource://greasemonkey/addons4.js"></script>
<script type="text/javascript">
if (typeof GM_addonsStartup !== "undefined") {
  alert("I smell a monkey!");
}
</script>