The problem here is that the links David has posted aren’t links as such – but links which should invoke a player embedded into the post. For whatever reason (and I’m not sure why), Firefox simply doesn’t want to display these as embedded videos at all. I can see them fine in Google Chrome – but the page then takes a while to load, because an embedded player has to be invoked for each one – not a good use of resources, I’d say.
Bottom line – the only way to post links to these videos that everybody can see is to post them just as links, and not embedded videos – which is what John has done.