It doesn't block youtube ads though, but it blocks everything else I've seen (or not seen ) so far on the web.
For NinjaKit, once installed, go to this page:
https://greasyfork.org/en/scripts/2984-viewtube
Click the green install button and that's it.
When you go to Youtube you'll now be presented with many download and playback options. Select the SD option click play and Quicktime will stream 360P in the browser - with no ads. You can go higher or lower depending on machine or choose to download the files.