Scratchpad for detecting unused CSS rules

uselessrules.js

var script = 'data:text/plain,' + encodeURIComponent(`
	let DOMUtils = Components.classes['@mozilla.org/inspector/dom-utils;1'].getService(Components.interfaces.inIDOMUtils);

	for (let ss of content.document.styleSheets) {
		if (content.matchMedia(ss.media.mediaText).matches) {
			content.console.log(ss);
			for (let r of ss.cssRules) {
				rule(r);
			}
		}
	}

	function rule(r) {
		if (r.selectorText) {
			try {
				for (let s of r.selectorText.split(',')) {
					let t = s.replace(/:(hover|:before|:after)/, '');
					if (!content.document.querySelector(t)) {
						content.console.log('[' + DOMUtils.getRuleLine(r) + '] ' + s.trim());
					}
				}
			} catch (ex) {
				content.console.error(ex);
			}
		} else if (r instanceof content.CSSMediaRule && content.matchMedia(r.conditionText).matches) {
			content.console.log(r);
			for (let rr of r.cssRules) {
				rule(rr);
			}
		}
	}
`);
gBrowser.selectedBrowser.messageManager.loadFrameScript(script, false);