Event Handling

Window.event does not exist in Firefox. Different browsers have different event models. Firefox handles the events slightly different IE and Chrome and for that reason it has not worked. A work-around is to pass the event as an argument to the function:
<a onclick="testfunction(event);">
 //...
</a>

testfunction(e){
 evt = e || window.event;
 //...
}
or use a library like jQuery to avoid dealing with all the differences between the browsers.