• The Greasemonkey Wiki has lots more information

Gmonkey comes with some builtin functions to store data inside the Firefox profile for use across multiple sessions, logging, and handling AJAX requests (getting more information and inserting it into the current page, without actually loading a new page – partial updates)

http://wiki.greasespot.net/API_reference

Important functions:

• GM_getValue – get a stored value
• GM_setValue – set a value
• GM_listValues –
• GM_log – output a message to the Firefox error log (can also use Firebug)
• GM_xmlhttpRequest – fetch remote data; is *not* limited by the Firefox same-origin policy, allowing you to pull in data from anywhere (!)

Next: Compiling Greasemonkeys into Extensions