If you are using new Yahoo! Mail beta sure you know the skyscraper advertisement at the right side when you visit your inbox.Personally i have no problem with ads cause they keep most services free for us but if they don’t move or flash around.
Yahoo! Mail Team now gives us the option to close that ad, for doing this you can click the arrow next to the ad to minimize the whole section. You must also know that it only stays closed while you’re viewing that email.
Thanks Yahoo!