how can I export pictures from facebook to IPhoto?

You can download (or used to) your Facebook profile. Perhaps that then leaves you with your photos on hand. Then just add them to your iPhoto.

http://www.mydigitallife.info/how-to-download-personal-facebook-profile-informat ion-to-computer/

Right click (or Control key + click) on the picture and save to the folder of your choice and then add them to iPhoto.