Now, Facebook provides you with the ability to experience Facebook entirely over HTTPS. You should consider enabling this option if you frequently use Facebook from public Internet access points found at coffee shops, airports, libraries or schools. The option will exist as part of our advanced security features, which you can find in the "Account Security" section of the Account Settings page.
There are a few things you should keep in mind before deciding to enable HTTPS. Encrypted pages take longer to load, so you may notice that Facebook is slower using HTTPS. In addition, some Facebook features, including many third-party applications, are not currently supported in HTTPS. We'll be working hard to resolve these remaining issues. We are rolling this out slowly over the next few weeks, but you will be able to turn this feature on in your Account Settings soon. We hope to offer HTTPS as a default whenever you are using Facebook sometime in the future.
Adding to secure browsing, there is also a security feature called as Login Notifications under which you will receive a email when your account by a new computer or device.
Courtesy: Official Facebook Blog
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