So you're saying when you click the button, the text of the textbox is set to 'unbelievable' and within the same event, you redirect to another page?

First of all, I can see no conceivable reason as to why you would want to do that: populate a textbox and then redirect. Why even populate it?

Second, this is happening because firefox is reloading the page from the server, while IE is giving you the cached version of the page.