I'm currently using the latest version of Firefox...

I got so fed up with the intromercials preceding
Youtube videos(especially the most annoying
and incessant one of the guy from sixpackabs
+intermittent fasting) that I searched for a way to
prevent those--irritating and totally irrelevant to the
content I was researching--ads from interfering
with the material in which I was really interested...

The first add-on I installed, AdBlock Plus, failed to
accomplish that goal. I promptly removed it.

The second one, Adblocker Ultimate, has so far
proved successful. I hope its performance continues
to do so.