I ported Alisdair McDiarmid's bookmarklet[1] to an add-on that will hide sticky content on a site. There was already a Chrome equivalent, but nothing for Firefox. It can be found here: https://addons.mozilla.org/en-US/firefox/addon/kill-sticky/
It's especially handy these days with the influx of cookie/GDPR agreement overlays, or app download dickbars[2].