Awesome RSS is a great extension, and is compatible again with Firefox 64+ and now adds direct subscription feature to Feedly, Inoreader, NextCloud Reader and even Tiny Tiny RSS (or universal feed display. https://addons.mozilla.org/fr/firefox/addon/awesome-rss/

Another great new extension is Want My RSS because it's compatible with 10 RSS readers for direct subscribtion (you can add your own when you have a self-hosted reader for example). Feed detection and feed display is also great! https://addons.mozilla.org/en-US/firefox/addon/want-my-rss/