Well, setting your adapter into promiscuous mode will allow you to capture all the packets. By using Ettercap though to put your adapter into promiscuous mode, it will handle the packet forwarding for you. Therefore, you can use Firesheep to monitor the entire network pretty easily.
From what I've seen it should capture them from everyone on the network, since Firesheep is simply capturing packets from whatever the adapter sees over TCP port 80. I haven't tried that yet, so you might be right.
Also, an attacker can simply use SSLStrip and get the cleartext passwords for online services anyway. This isn't anything novel, since there have been plenty of attacks that allow you to session hijack rather easily (i.e. hamster). You can even simply monitor in Wireshark and manually enter the session information into your cookies.
From what I've seen it should capture them from everyone on the network, since Firesheep is simply capturing packets from whatever the adapter sees over TCP port 80. I haven't tried that yet, so you might be right.
Also, an attacker can simply use SSLStrip and get the cleartext passwords for online services anyway. This isn't anything novel, since there have been plenty of attacks that allow you to session hijack rather easily (i.e. hamster). You can even simply monitor in Wireshark and manually enter the session information into your cookies.