Now I will tell you how can a hacker use firesheep to hack a facebook or any other account, You will need the following things:
1.Public wifi access ( If you want to do some Gud prank bcz you knw i am white hat not recommend black hat activities)
2. Winpcap ( If you have nMAP Insatlled then you dont need to Install It )
3. Firesheep ( Google It I Dont Think It's very Difficult To get It )
There are mainly three steps to Go for it
1. First of all download "Firesheep" from the So called Google :P and use the "openwith" option in the firefox browser
2. Once you have installed firesheep on firefox web browser, Click on view at the top, then goto sidebar and click on Firesheep.
3. Now click on the top left button "Start capturing" and it will start to capture the session cookies of people in your wifi network, This will show you the list of those people whose cookies are captured and have visited unsecured website known to firesheep, Double click on the photo and you will be logged in instantly.
Before it i was using Cain (Sniffer) for windows platform. But for Https Environment Big no So this works. So Chillllll WipSy ZipSY .