The extension uninstalled is not breaking YouTube, in fact while it is installed it is the only thing making it work for users that are being affected by a YouTube bug: https://www.reddit.com/r/youtube/comments/diy07n/bug_the_video_loaded_like_this_and_ran_at_about/

And you can roll back to the previous extension version, they are always available in the version list: https://addons.mozilla.org/firefox/addon/particle-iridium/versions/