Off topic: I don't know a single feature that would be as annoying as fucking toolbar/header/whatever showing up when you scroll upwards. Why everybody does this?
I agree, although, it’s not as bad in this case. I find it far more annoying on sites where the header is always there, as it breaks page down / spacebar functionality (when you page down, the header will cover some unread text).
Makes sense in Facebook mobile app, where you often actually want to use the toolbar (it lets you create a new post). Elsewhere, I don't know. Probably people copying UX solutions from other people without thinking about whether they're needed.
