Recently I came across Facebook Resource for Akonadi which makes events, contacts, notes and messages from Facebook available in KDE. In other words you are able to see your Facebook friends through KAddressbook and their birthdays as well as Facebook events in KOrganizer. Moreover events and birthdays are also shown in the Plasma clock calendar. All this data is available offline thanks to Akonadi. So let's take a look on Akonadi-Facebook.
For Archlinux Akonadi-Facebook is available in AUR. You can easily install it by using yaourt.
If you are using another distribution search for a package named akonadi-facebook. In case you don't find it you will have to build it on your own from source like this:
git clone git://anongit.kde.org/akonadi-facebookcmake -DCMAKE_INSTALL_PREFIX=`kde4-config–prefix`make install
Once you have it installed press Alt + F2 and run Akonadi Configuration
In the Akonadi Server Configuration tab press Restart to load the new resource you have just installed.
In the Akonadi Resources Configuration tab press Add and search for Facebook.
Type in the account name, something like Facebook.
And then press Authenticate. Here you will have to login your Facebook account and allow this app to access your friends, events and messages.
It will also ask you to access your data at any time.
If everything goes well you will be authenticated.
And the resource will show a ready green icon.
Now open KAddressbook. You will see a Friends Address book with the Facebook logo. All your friends are listed here.
Next open KOrganizer. Here you will see an Events calendar with the Facebook logo. The events and your friends birthdays will now be displayed in your calendar.
Have in mind that this is an early application version. However I didn't encounter any problem while using it