General :: Retrieving A Public RSA Key Through The Command Line?

I'm doing a project demonstrating weaknesses in facebook's security setup, and I've reached a bit of a roadblock.I need to retrieve the public RSA key of the website (facebook) that it uses for https traffic. I know I can do this through firefox and everything, but I need to do it through the command line. If that's possible, that would be great, and would lead me to question number two. Once I have the public key, how would I use it to decrypt raw network traffic, like from wireshark, that came from facebooks servers that was encrypted using the public key?