If you already had some YouTube page open before the extension was installed, a page refresh might be needed. The kind of ads that will be closed for you, is the same as you would have to close manually. Specifically: - Video ads, that can be closed with "Skip Ad" or "Skip Ads" button - Banner ads, that can be closed with "X" button When are the described ads loaded, the button to close the ad is prepared too, although, to you, it is shown after a delay. As a result, the extension can close the ad sooner and faster. The ad can appear for a quick moment only.