A new add-on for Firefox makes it easier to hijack e-mail and social networking accounts of others who are on the same wired or wireless network. Most online services use secure sockets layer (SSL) encryption to scramble the initial login. But with many sites like Twitter and Facebook, subsequent data exchanges between the user and the site are sent unencrypted and in plain text. The only effective fix for this problem is full end-to-end encryption, known on the web as HTTPS or SSL.”]
Source: https://krebsonsecurity.com/2010/10/firesheep-baaaaad-news-for-the-unwary/