We have checked this through FireFox and the videos play as intended. Please go here and double check that your Flash player is enabled: https://helpx.adobe.com/flash-player.html
Also if possible can you please provide some of the videos you have opened and do not play so we can investigate this further? Thank you!
An error occurred while saving the commentrandpat commented
Same problem some videos play and others play sound with no audio. Used Firefox and Chrome on my mac.