Well, the inconsistencies between browsers is quite a good point if it would cause inconsistencies in user experience. I'd like to point out, however, that FB

Well, the inconsistencies between browsers is quite a good point if it would cause inconsistencies in user experience. I'd like to point out, however, that FB already does some kind of similar trick with the URL hash when browsing photos: if you open someone's photo, it'll open in a modal dialog where you can navigate to other photos and this in-page navigation _will_ change the URL hash. If you go to that modified URL directly (or refresh the page) FB will show a different page (inside the person's "album") with that photo. I'd reason that, for FB, a photo is more of a tangible thing than an item in your infinite stream, thus it deserves separate URLs when browsing the them.