Don’t know what’s going on with QuickTime – maybe a fallback if your browser won’t play h.264? Does it work on Chrome without QuickTime?
(– edit: Three people [who downvoted me] seem to think that formulating a reasonable hypothesis and asking reasonable questions because of conflicting information is already too much Apple love. Or maybe they just think I’m lazy for not doing the research myself? Oh, well. Check out my other grandkid comment in this thread to see how testing my hypothesis worked out.)