I just now "Saved & Exit" and when I clicked "Resume Game" the ad was gone. Try it next time.
Simple answer don't play by clicking on play now. Set your browser start page to the game client.That way you can block pop-ups.
I had that problem for a while. I now use an ad blocker (I recommend Adblock Plus). It is free, easy to install, and solved all my problems.
Hope this helps.
About 4 years late, but ......
gerryniswonger: I just now "Saved & Exit" and when I clicked "Resume Game" the ad was gone. Try it next time.