Another option for users is to put

    javascript:(function(){var st = document.createElement('link');st.type = "text/css";st.href = "https://raw.github.com/Primigenus/Cleaner-Hacker-News/master/cleaner-hn.css;st.rel = "stylesheet";document.body.appendChild(st)})()

in a bookmark (e.g. on the bookmark bar), then just click it when they want a "cleaner" HN.

Avoids having to install anything extra, but you will need to click it every time you want to use it.