Many sites just don't bother to assign focus to the main content region. (I don't think they even realize they're doing it wrong.) Page up/down work if you firs

Many sites just don't bother to assign focus to the main content region. (I don't think they even realize they're doing it wrong.) Page up/down work if you first mouse-click there, assuming you can find a place to do that without the page hijacking it.