resolved: the problem lies on Google DNS. Facebook's images are on akamaihd servers that are selected geographically as closest to you. this is done using your DNS. if you use Google's DNS (8.8.8.8) it gives akamaihd the wrong location (maybe India.. and I am in Italy) and as a result all Facebook contents are so slow to display that it becomes unusable.
Solution is changing your DNS to your provider's.