This add-on was absolutely amazing. It, alone, justified my changing browser to Mozilla. It worked perfectly.
Unfortunately YouTube also found it worked perfectly, and recent massive upgrades on YT now recognise it.
If you don't disable it, YT disables your browser and locks you out after 3 vids. So I've had to disable it until Adblock produces an update.
I'd forgotten how really annoying YouTube is for ads... until now!