differences between running firefox on windows xp and vista

Very strange, I have installed the countdown module and when I view my site via firefox (3.0.1) on a computer running windows xp professional (version 2002, service pack 3) the timer counts down the seconds in real time. When I view site with firefox (3.0.1) Vista (home premium, service pack 1) it only displays accurate countdown on refresh.

Also, note that I did modify countdown.tpl.php, but only to change display text, eg "Days" to "DAYS"

Weird.