I didn't do it. Any suspects or motivation yet? http://sanfrancisco.cbslocal.com/2016/05/20/police-investigate-firebombing-at-google-headquarters/
Is there a difference between a bomb and a firebomb?
Bombs aren't designed specifically to start fires, ie in Israel. My guess is the I/O conference brings extra opportunity for attention.
My money is on a privacy extremist group (and I think I just coined a new phrase maybe; lets see if it catches on).
I am not familiar with that complex, but I would imagine someone is going through security recordings right now. There are cameras etc everywhere. Unless you have a cloak of invisibility, expect yourself to be captured on camera when visiting Google campus.
Probably just some stupid teenagers.