It would depend on how you set-up you .co.cc domain. If you set it to point to the x10 Nameservers then the favicon will work. However if you set it to URL Forwarding then it'll be the .co.cc favicon that is shown.
I suggest setting up your .co.cc domain with the x10 nameservers, it is easy to do, and means that .co.cc can't mess with your page.
First make your domain as primary in the account panel as suggested by techash
But not sure whether you need to do that or not
but do the below instruction ..
Upload your favicon icon and add this piece of code to your page.
<link rel="shortcut icon" href="images/transparent.ico" >