In some cases, a MOV file that's posted in the forums is embedded using the outdated object tag, and not the standard video tag.
When this happens, the file will not play when the user clicks on the video, and it may not be obvious how to play/download it at all. This applies to both Mac and Windows users.
e.g. Someone posted a MOV video [probably recorded on their iphone], and it's not directly playable by left-clicking on it, even on Apple platforms: