how to map the js file location to another location?

When I visit the stackoverflow.com website, I cannot load http://ift.tt/t0Y3fx. Therefore the speed is too slow to visit this website unless using VPN. I hope that when my browser is loading http://ift.tt/t0Y3fx ,it will automatically load http://ift.tt/1JuEjQq instead. I tried to change the host file in C:\Windows\System32\drivers\etc,I added "120.52.19.44 ajax.googleapis.com", but it did not work.(120.52.19.44 is bound to libs.useso.com). Is there any method that can make it work? I have an idea which is caching the js file permanently, but I don't know how to cache it manually.