Finally, after two years from the first release of the feature and hoping that the users will switch to https, Facebook enforces now https to all users by default. This feature means that your browser is told to communicate with Facebook using a secure connection, as indicated by the “https” rather than “http” in https://www.facebook.com.
This uses Transport Layer Security (TLS), formerly known as Secure Sockets Layer (SSL), and makes the communication between your browser and Facebook servers more secure.
According to Facebook, more than a third of users had enabled the feature following its introduction. The option could not be activated for all users from the beginning because of technical difficulties. For example, enabling TLS will basically double the time of downloading the content from the website. In order for the redirect to work for most users, Facebook had to tweak a lot of things which can be seen in the original post.
For the normal user, this means more security with a minimal cost of slowing down a bit the browsing. TLS/SSL prevents man-in-the middle attacks which could steal login cookies and pretend to communicate with Facebook as the user.
The best part is that no user has to do anything.