It's part of how yahoo feeds you ads so try going to adblockplus.org with your browser and install the adblock plus add-on. When you install it there should be an option to also remove acceptable ads - make sure you tell it you don't want any ads.
Restart your browser and then go to yahoo and see if that helps. When I go to yahoo it still looks for .ying.com so if it doesn't help try removing all of your yahoo cookies. Click on Firefox in the upper left (Or Tools if you have XP) then on Options, Options, Privacy, Remove Individual Cookies, search for yahoo and then delete any you find. You will probably have to login again to yahoo so hopefully you know your password.
Also I don't use yahoo but I am seeing a lot of script timeouts on my gmail in the latest version of Firefox so it may be a Firefox problem. Have you tried Chrome?