Ask HN: What are the most useful Firefox addons?

Because I'm always tired of seeing Chrome promoted as the defacto browser and ecosystem, here are my favorite Firefox addons:

Ghostery - http://www.ghostery.com HTTPS Everywhere - https://www.eff.org/https-everywhere Cloud To Butt Plus - https://addons.mozilla.org/en-US/firefox/addon/cloud-to-butt-plus/