How To Get Rid of This Adware On My Mac

I keep getting these pop-up ads on YouTube. At first I thought it was another annoying thing YouTube was doing, but it's only happening on ONE of my MacBook pros. My other MacBook is fine. I get these ads in other ways too. Does anyone know what it is and how to get rid of it? Attached is a screenshot.

http://www.flickr.com/photos/99112939@N02/9323605454/lightbox/

Those are embedded ads in the content. Not all content has those ads. When you notice those ads, take a look at the slider - you'll notice an orange (I think) mark on the slider which is the point in the video where those 3rd party ads will pop up.

When you find a way to block those, let me know.

Those are placed there by the content creators - to make themselves money.

Thanks Bobtomay, but with all do respect I don't think that's correct. Those ads appear on EVERY YouTube video I play, BEFORE the video plays. They're also appearing over some flash content on some websites. It's not just YouTube. And like I said in my above post, this only happens on ONE of my Macs. This is obviously something that has infected my Mac. Below are links to two other screenshots of where these weird ads are appearing.

EXAMPLE 1
Example3 | Flickr - Photo Sharing!

EXAMPLE 2
Example2 | Flickr - Photo Sharing!

Things to look at - any browser tool bar you've added along with add-ons and extensions.