Ok, interesting. Can you tell me which web browser you use?
The reason I ask is, because our computer screens are landscape, portrait photos need to be resized more aggressively to fit on screen. And some web browsers are better than others at on-the-fly image resizing, you see. So I'm wondering if that's the reason you're seeing a problem on your screen, when I, as I browse your FB photos, can't see a problem on mine.