how does adblock work?
It blocks pretty much every ad from even loading.
No banners, no pop-ups, no floating flash ads.
Not sure about pre-video youtube ads though. I have never had one, but I don't know if it's just because of the video's I watch or the adblocker.
Then there are also script blocking that stops scripts from running which will also block lots of unwanted thing from loading on your machine.