I don't know how long this has been going on, as I don't use Facebook regularly. But for some reason when using Facebook on Safari I am unable to Expand Comments or click the Notifications button at the top of the screen. It shows the scrolling 'loading' bars or toggles the notification button when I click it, but nothing happens. I've done a Reset of Safari and the problem persists. When I switch to an alternative browser such as Google Chrome I no longer experience the problems.