If you're anything like me you block ads in EVERYTHING possible. Today I realized there were some sneaky ads that I had been ignoring in Youtube vids that pop up along the base of the video. Most of the time I click to close it but ocassionally I leave it there because it's almost as annoying having to click it as it is having it there in the first place. Enter Tubestop, it's a lightweight firefox extention that blocks those pesky ads.

https://addons.mozilla.org/en-US/firefox/addon/6648

Now, the original intention of Tubestop is to stop the automatic playing of videos so you can open multiple youtube tabs without having to worry about them all starting up at once. A lovely side effect of this though is it bypasses Youtube's player. So keep in mind you'll still have to click, but just on the video to get it to play.