not able to watch video on website

try typing this in the address bar

about:plugins

This will show you all the plugins that firefox is currently using, and you can check who is handling the flash files.

My best guess is that you have something else handling the flash files. Post the results so we can check it out.

Perhaps you need plugin for playing videos embebed on firefox, i recommend the install of mplayerplug-in:

sudo apt-get install mplayerplug-in

http://mplayerplug-in.sourceforge.net/

Try
http://get.adobe.com/flashplayer/

That should sort out YouTube but for the rest of the multimedia you might want to work through

https://help.ubuntu.com/community/Medibuntu

Good luck and regards from
Tom :)

this results i get by typing in address bar.
Shockwave Flash

    File name: libgnashplugin.so
    Shockwave Flash 8.0 r99. Gnash 0.8.2, the GNU Flash Player. Copyright © 2006, 2007, 2008 Free Software Foundation, Inc.
    Gnash comes with NO WARRANTY, to the extent permitted by law. You may redistribute copies of Gnash under the terms of the GNU General Public License. For more information about Gnash, see http://www.gnu.org/software/gnash. Compatible Shockwave Flash 8.0 r99.

MIME Type Description Suffixes Enabled
application/x-shockwave-flash Shockwave Flash swf Yes

try removing gnash and installing the non free plugin:

sudo apt-get purge gnash

sudo apt-get install flashplugin-nonfree

problem solved by downloading adobe plugin

Brilliant, nicely done :))))
Congrats and regards from
Tom :)