Google, Facebook, Apple, Microsoft. And, no.
Sure, the ones you mentioned have the biggest paychecks. But they won't give you indemnity and extended resources to find weaknesses in critical infrastructure. Some people like breaking bigger toys.
I'd actually say security research firms have pretty high quality security people, however, and not just the tech giants.
1. http://www.iphoneincanada.ca/news/1password-open-letter-bank...