Your Facebook Login is one of the details hackers are very keen to get hold of as the social network is the most popular in the world, including the UK.  So accessing this as you is a prime tartget if you use an unsecured connection.

A firesheep user can find any unsuspecting victim and provides a picture of the user with a button next to it allowing them to log on as the person.

The only real way to solve this issue is for the site to offer full end to end encrytption better known as HTTPS or SSL.  The websites only encrypt the login stage of the site the rest is a fully open session when cookies and session IDs can be easily viewed by a hacker, so little can be blamed on the WiFi hotspot. The hacker simply hijacks the session and can interact as the users but in most cases not change information as this requires a password.

You can tell if some one gets targeted as the following is usually left in the status update ' I was facebooking on the public WiFi and all I got was this lousy status update'.  So keep an eye on the sites you are using and make sure you login with caution.  You can also let them know that encryption is important to you and your privacy depends on it.  Also look for any add ons to you browser which enforce encryption.  Or alternatively only use a VPN. Good Luck