This add-on has been finally updated after two and a half years! It was dysfunctional in some areas, i.e. the Web Clipper couldn't save YouTube-links anymore (the Chrome version, of course, would always get updated). As a customer paying for their premium service, this negligence on Firefox was pretty infuriating. I'm thankful that this add-on works as intended again and hope that Evernote does not drop the ball again in the future.