Not going to give every thing, read manual. Just outline. Ping http://www.google.com to get ip of google. In firewall filter rules make rule accepting google ip in dst address and after that rule that reject ip 0.0.0.0/0 in dst rule. Important not Src rule or you will lock out yourself .
I would however suggest you use proxy, very easy to reroute every web page to go to google instead, no matter what web page are entered in browser. This way no page unreachable error, just google page.