I've had a similar problem, and "solved it" by just using a link:
<a href=contacts.csv>Click here if you are using that fould piece of excrement, the IE for the mac.</a>
It's a Mac IE problem: Safari, Netscape 7.1, etc. work as advertised. Mac IE is very, very slow and very, very buggy, and if you are using javascript code that works on the PC, test it, test it, test it, as it will probably break on the Mac.
Wean your user from Mac IE and use some other browser. They will thank you. MS has stopped supporting IE for the mac.