First of all we need to go to the Doodle page. This is not the Google home page as there the code is more complex and we want to focus in the relevant files. The URL is http://www.google.com/logos/2013/bday13/bday13.html
There we can see they are loading a file, bday13.js which is obfuscated and minimised. This makes the analysis a bit harder but we can try some tricks in order to make our job more easy.
We start with 10 “hits”, so we can do a assumption and do a search for “= 10;”. Go, do it now… you will be pointed to just one occurrence of this pattern inside the code.
But wait! We still have Firebug and Firefox’s built-in Web Developer tools. So we can set up a breakpoint when bd is set to 10, increase it to 50 and start a new game. It will be difficult not to get a high score!