Strict Transport Security is a great solution to protecting against Firesheep
Now ultimately the vulnerable website is supposed to fix this issue on their side. But, let's not wait around for them. Let's fix it on our side and protect our traffic now.
Step 1: Grab a browser that supports Strict Transport Security (Firefox 4 & Google Chrome both support STS)
Step 2: Install an addon that lets you add specific STS settings - STS-UI
Step 3: Configure STS-UI for the sites you're concerned about
Step 4: Be happy your data is more secure. However, securely transmitting data is only one piece of the security pie. But at least you're good in that department.
Go to tools->Manager Strict Transport Security
After adding facebook.com and twitter.com it should look like this
Done. Now you will always be using HTTPS for data exchanged between twitter or facebook.
Remember, this only protects you against sites that are either already using STS or sites that you have manually added. This really isn't a scalable approach since xyz.com could be vulnerable and you wouldn't know unless you inspected the traffic going back and forth.
For those that have access to company VPNs or SSH tunnels for their traffic, I'd recommend you also use those when accessing the network from a wireless hotspot. A VPN doesn't solve the problem, but it does remove access from the likely attackers (e.g. other random users of the wireless hotspot).