Historically, no tech company stays in the #1 spot for more than a decade. That doesn't mean Facebook won't be around in 10 years, but it does show how volatile the tech market can be.
XBox was viewed as a joke but they kept at it with their cash machine, and now they're successful.
Dreamcast was awesome but they didn't have the cash to keep at it and had to throw in the towel.
If google keeps at it, they'll sink or swim, but you have to be persistent to try to take that share.
Personally, I think google hires at a far more talented tech pool. They're doing things like VR glasses and automatic parking cars while facebook makes a big deal about integrating with Skype. So the talent is there. The money is there. The marketing is there.
We'll see how this plays out. I'm excited to see the outcome.