This is a Thunderbird extension to draw attention to e-mails that are simulated phishing attacks.
My employer regularly conducts simulated phishing attempts, and rewards employees who correctly report such phishing attempts with entry into raffles, despite the risks of giving attackers a magic header that can let messages through any other protection and that training via simulated phishing exercises has been shown to be ineffective.
This extension is intended to indicate such e-mails to me so that I report them instead of simply just deleting them. My stance here is that all this extension is doing is either pointing out fake phishing attacks or that it is pointing out real phishing attacks pretending to be fake phishing attacks, and in either of those cases deleting or reporting such messages is the correct action. It does not provide any additional coverage for real phishing attacks that do not pretend to be fake phishing attacks, but you were on your own for those anyway.