fixfa.user.js

// ==UserScript==
// @name           FixFA
// @namespace      http://labs.henriwatson.com/greasemonkey/fixfa/
// @description    Change the amount of screen space FA uses.
// @include        http://*.furaffinity.net/*
// @include        https://*.furaffinity.net/*
// ==/UserScript==

(function() {
	// Detect Firebug
	if (document.getElementsByTagName("div")[0].id == "_firebugConsole") {
		content = document.getElementsByTagName("div")[1];
	} else {
		content = document.getElementsByTagName("div")[0];
	}
	// Change the CSS for the div we hooked onto
	// The end result should be this "position: absolute; width: 80%; left: 50%; margin-left: -40%;"
	content.style.position = "absolute";
	content.style.width = "80%";
	content.style.left = "50%";
	content.style.marginLeft = "-40%";
})();