It can't work on ALL of them. However, let me copy-paste the message from the extension's homepage:

The GDPR is a European Union (EU) privacy law that will affect businesses around the world when it becomes enforceable on May 25, 2018 - meaning, tomorrow!

Many websites are implementing or changing their cookie notifications right now to meet the deadline, so you may see them more frequently that usual, even on bigger websites and websites from the US.

Don't worry and please be patient, these new notifications will also be blocked in the next version.