Essential extensions for online reading:
Bypass Paywalls (removes paywalls from news sites)
https://github.com/iamadamdev/bypass-paywalls-firefox
Medium Unlimited (removes paywalls from Medium)
https://addons.mozilla.org/en-US/firefox/addon/medium-unlimited-read-for-free/
Make Medium Readable Again (removes nagware from Medium)
https://addons.mozilla.org/en-US/firefox/addon/make-medium-readable-again/
View on Sci-Hub (redirects paywalled journal articles to the same paper on Sci-Hub)
https://addons.mozilla.org/en-US/firefox/addon/open-on-sci-hub/