mek's YouTube Ad Skipper — mek

It should work by default but there is a way to update it (if YT changes something).
1) Wait for the Skip button to appears
2) Click to Skip
3) Click on the Extension icon for this extension
4) On the popup, left click on the class you want to add (probably something about ad, button, ...)
5) That's all, next ad will be automatically skipped