I need to detect the user's active browser extensions / add-ons

Question

I don't want my website user to download my protected Vimeo videos - there is a couple of extensions that can download the video regardless of what I do.

How can I detect if the user is using them and redirect that page to somewhere else.

Answer 1

You can't know the extensions the user have. As Mozilla said:

You can't check for extensions that are installed. Plugins can be detected via navigator.plugins as you posted, but you can't detect extensions for privacy and security reasons.

As a general rule, if it's on the Internet, users will be able to copy the content. You can make the content harder to copy, but it's almost impossible to come up with a perfect solution.