Here’s an easy way to test it, after installing it and activating it.
I start an “New private window” in Mozilla Firefox (or “Incognito Window”) in Google Chrome, and I should see a notice at the bottom. If it works, it looks like this:
The new window needs to be incognito, because it’s possible that, in the regular window, you already agreed with the cookies, and the message is displayed only once. Using incognito mode, you force the notice to appear again.