NoFollow：
https://addons.mozilla.org/en-US/firefox/addon/nofollow-advanced/
SeoQuake：
https://addons.mozilla.org/en-US/firefox/addon/seoquake-seo-extension/
Ahrefs SEO Toolbar：
https://addons.mozilla.org/en-US/firefox/addon/ahrefs-seo-toolbar/
SEO & Website Analysis：
https://addons.mozilla.org/en-US/firefox/addon/seo-website-analysis/