The Greasemonkey Compiler is an online tool that can be used to convert Greasemonkey userscripts into Firefox add-ons. One of the main advantages of Firefox add-ons is that they do not require the Greasemonkey extension to be installed. This makes it also easier to distribute the script.

The Greasemonkey Compiler is a simple web form. Some of the needed parameters are already filled out automatically including a random GUID and the compatible Firefox versions. They can be edited easily to keep the Greasemonkey script compatible with future Firefox versions.

All that needs to be done is to paste the complete source code of the Greasemonkey script into the User Script text form on the website. A click on Compile will create a Firefox add-on based on the uscript with the xpi extension. This add-on can then be installed in the Firefox web browser where it will provide the same functionality that the Greasemonkey script would offer.

There are two problems associated with the conversion of Greasemonkey scripts into Firefox add-ons using the Greasemonkey Compiler. Options that might have been provided by the Greasemonkey script are not carried over into the Firefox add-on. This can be problematic for some scripts that can be configured. The second problem is that the script has to be updated manually by performing the same conversion with a newer version of the script.