A good little piece of software. Easy to install, do one thing and doing it well. About the punycode, look at https://www.xudongz.com/blog/2017/idn-phishing/ and don't forget to tweak "network.IDN_show_punycode" in about:config (set it to true) and do the test again.
Runs nicely, is pertinent (necessary and well carried out). The ESIEA_CNS-CVO is no fantasy, a serious engineering institute and the add-on performs certificate comparison/checking quickly and -- most appreciated -- on the user's demand only (no background automatic/systematic checking, which I dislike/avoid when not required). Nice work and required IMO when we are aware that https itself may happen to be a falsified passport... I check whenever a doubt and systematically on https sites handling my data.