When playing a video on YouTube the light-red buffering progress no longer appears, though the rest of the UI works as usual. Buffering still happens, it just doesn't display its progress.
I'm not sure if this is intentional by YouTube or not, but in any case, how can I make it visible again?
I'm using Firefox on Windows 7, with Flashblock, as a signed-in user. Trying the recommended solution by Google to generic YouTube problems - which is emptying the browser cache - didn't help.