The `userstyles` module allows one to load css/userstyles for content or chrome pages. ## Example ## // loads a user stylesheet require("userstyles").load(require("self").data.url("style.css")); @function Loads css (aka userstyles) to the browser which will be automatically removed when the add-on unloads. @param url {string} The url of a css file. @param options {object} Some options for the stylesheet. @prop type {String} The type for the stylesheet, there are two types 'agent' and 'user'. The default should be used when possible, which is 'user'.