The Busy moon user stylesheet displays the phases of the moon while you wait for a web page to finish loading, and can be installed in either Stylish, Greasemonkey, or userChrome.css. To see what this looks like, just open a couple Firefox tabs and view the image. See the tiny version of the big picture swirling in the tab bar? That’s what every page will look like while it’s loading.
Hey, while the topic is user s___s, I have like a million Greasemonkey user scripts that I never write up on the blog, so check ‘em out.