I tried out the example you linked to. What version of Firefox are you using?
On the example it says:
“This page has been tested with IE 6,
IE 7, IE 8, FF 3, Safari 4, Opera 9,
Chrome 4 “
I think the issue might have to do with what browser version or plugins you are using. I just tested it in IE8 and everything worked fine for me.
Short of that and without taking a look at your code or changing the plugin source, I am not sure we can help you resolve the issue.
solved jquery countdown timer