Mark at the MakeUseOf blog points out that it's become all the rage to convert Greasemonkey user scripts into Firefox extensions - giving our own Gina Trapani's Better Gmail as an example.
The benefit of this is that even non-programmers can take a Greasemonkey script and turn it into a Firefox extension - a format more likely to be used by non-programmers.
Mark runs you through how to use a User Script Compiler to turn a script into an XPI file (Firefox extension) - no coding required:
Once you've filled out that screen and hit compile, you're done - just drag it onto your Firefox browser to start the installation. As Mark points out, you can find new user scripts from sites like Userscripts.org.
How to turn Greasemonkey Scripts into Firefox Extensions [Makeuseof.com]