I think OP was suggesting that it's the responsibility of those companies to warn their users, etc. Not that it was the firesheep dev's responsibility.
exactly, it's MITM attack people have been able to do for at least a decade
That doesn't really make it less of a security threat. Sites still don't know how to secure it. On my own site we do the same, and have no other answer but end-to-end encryption which we then charge for.
I agree with this. How is it facebook's responsibility if the user's wireless network is unprotected? Of course the companies are silent. It's not their vulnerability and it's nothing new, it's been like that since forever. Encrypting all traffic for them is expensive and breaks functionality. What are they supposed to say, to warn users? Something along the lines of: "Warning, HTTP session hijacking has become REAL USER FRIENDLY recently."