I had that before, I remember. I think you can just google it and easily find a fix, get some ad-stopper or something, or maybe reinstall your web-browser.
That's probably some unwanted plugin you accidentally installed, just turn it off. For Mozila, just click 'Firefox' on top left, and then click Add-ons, then disable all Plugins.
its a legit program that dosent present itself as a virus i recommend http://download.cnet.com/AdwCleaner/3000-7786_4-75851221.html i use it myself when this shit happens
