Why not post a screen shot.

Whatever it is you are seeing is probably not connected with Firefox but something else you have managed to download.

That's probably a snippet on the about:home default homepage. You can change your home page to get away from the video.
http://support.mozilla.com/en-US/kb/How+to+set+the+home+page

thank you i will try to post a screen shot never done that before. i just assumed because it was a fox that it was from mozilla it says "play runfield the latest HTML5 from "Aurora "

thank again i will try that

The "snippetContainer" is what that part of the about:home page is called, in the internal coding. It is used by Mozilla to send different messages to users as they open Firefox. Most release versions rotate 3 or 4 different messages, but the 6.0 Beta seems to be stuck on that one HTML5 video message most of the time.

You can hide the box that shows the snippets with code in userChrome.css. if you want to hide that silliness.

Add code to userChrome.css below the @namespace line.

   * http://kb.mozillazine.org/userChrome.css
   * http://kb.mozillazine.org/Editing_configuration 

You can use the ChromEdit Plus extension to have easier access to the customization files.

   * ChromEdit Plus: http://webdesigns.ms11.net/chromeditp.html 

 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

/* hide snippet container on the about:home page */
#snippetContainer { display: none !important; } 

edit - fixed the code to display correctly

so i was right- the glitch is in the browser thanks again. has no one else posted the problem?

I guess I must have already opted for some option not to display such snippets. My page source shows:

<div id="snippetContainer">

       <div id="defaultSnippets" hidden="true">  

I am not seeing jumping foxes, even in Firefox 6.

I wonder has markup syntax of this forum been modified

I thought leaving a leading space allowed the less than chevrons of code, but I had to use the escape above.