I came up to a difference between firing events in internet explorer and firefox, Chrome, safari etc.
In Internet explorer 8 you can fire events like onclick, onmouseover etc with the method fireEvent with javascript. In other browsers you can use dispatchEvent for this and in some other libraries like Prototype you can use triggerEvent or trigger in jQuery.

When you fire an event in the standard browsers (FF,CHR etc) a submit on a form is triggered and a document.location change is triggered when an “click” event is called. And when you don’t want this to happen you should call preventDefault() to cancel the default action of the button or anchor (submitting or redirecting to an other page). But…. in IE8 I see that when calling fireEvent(‘onclick’) only the onclick listeners that are added to the buttons or anchors are triggered but NOT the default actions. So there will be no submitting or redirection when calling fireEvent(‘onclick’). But when you call the general click() function all the onclick event listeners will be triggered INCLUDING the default action. So try it yourself in this example with internet explorer.

See example on http://www.frontendplace.nl/bb/wp-content/uploads/2012/02/fireEvent-Method-Sample.html