theres a few things u can try, in the following order:
1) Minimize the window and then restore it. This might make a different ad show when u restore it, which might fix the problem. Much of the time, high CPU is caused by a certain animated ad, and when the bar switches to a different ad, the cpu returns to normal.
2) Get an adblocker, and when u get the CPU spike, minimize the window, turn on the adblocker, restore the window, and the ads should be gone, or they'll be gone once the current ads finish. (or just have adblocker on always, but fod doesn't appreciate that)
3) Download Process Explorer at
http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
Install it, and next time your CPU spikes, open process explorer, and look for the thing with the highest CPU % next to it. If it's your browser, then the ads or the game is the problem (hopefully just the ads). If it's not your browser, then there's a good chance it's either svchost or "help and support." If help and support, just close it. If svchost, right-click, then click Properties, then click Threads, then see which has the highest % and tell me which one it is. If it's none of the programs/services i said, and if ur not sure what it's for, tell me what it is.