Detect Browser Extensions?

Unfortunately the links you shared are not related to how to have a website detect what extensions are installed in a users browser.

There is no way for a website to do this kind of detection mainly due to privacy concerns as you would be able to get a list of every users extensions and by so also potentially track and collect data about specific user behavior and more.

An extension however can alter HTML on a webpage, making it look like the website detected the extension, when it was actually the opposite happening.