[eluser]sikko[/eluser]
Codeigniter is ran Serverside, That means all the page is fully rendered before it comes back to the browser.
That means the redirection shoudln't be affected by the browser you're using.
At first blush, it looks like a Javascript problem. Which could indeed change depending on the browser you're using, and especially on IE [which is the worst browser ever].
Could you tell us how you make your redirection php/js ? could we have a piece of code ?