So perhaps it's time to install one?

Try https://addons.mozilla.org/firefox/addon/ublock-origin/

Are you possibly running Firefox in (permanent) Private Browsing mode (Always use Private Browsing mode; Never Remember History)?

• https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history

Can you at least explain what is the problem? Does YouTube uses this trick to force people to buy the premium or just to censure them? There is a lot of thing going around in the world and people's comments are sometimes not appreciated by some people.