Is it supposed to play? I'm just getting a single static image. (Firefox 37.0.1 on Ubuntu)

Edit: Plays on my Android phone.

How close was that !!! Unbelievable ...

For reference and completeness, works in Chrome.

Refreshing it seems to fix it

Tried that - didn't fix it.

I have now watched it on my phone and it's amazing. I'm just a little put out that it doesn't work on my up-to-date install of Firefox on my up-to-date install of Ubuntu.

Is there a version of Linux that really does "just work" ?

Try clicking on the image.

I did - it doesn't.