Firefox and htm5: "Your browser does not currently recognize any of the video formats available."

[jd1008]

At url youtube.com/html5
I request the html5 player
then I play a youtube video.
I get the message
Your browser does not currently recognize any of the video formats 
available.
Click here to visit our frequently asked questions about HTML5 video.

Clicking on the link, shows that only
HTMLVideoElement and WebM VP8are check marked .

The rest are red squares with a white bang in them.
Is there a way to ask youtube to select a different format of the video
other than what it chooses by default?