Lost data if using Server.Transfer method only in IE, not in firef

Hi all,
Our asp programs seem to have different behaviors when users use IE and
firefox.
One of most annoying things is the data disappearing problem in IE but not
in firefox.(Note: Sometimes a search program can run much faster in Firefox
than in IE, don't know why)
For example,
I have an internal user interface which they can do different product data
entry,
the program will use Server.Transfer to different asp program for data
entry. Here is the code.

Page1---UserInterface.asp
Select Case Request("Product")
Case "Sel"
Server.transfer("/Virtualdir1/test1.asp ")

Server.Transfer("/Virtualdir2/Test2.asp")

Case "Bear"
Server.Transfer("/Virtualdir3/test3.asp")

Case "IMED"
Server.Transfer("test4.asp")

Case "AC"
Server.Transfer("/Virtualdir4/test5.asp")

Case Else

End Select

When user finished data entry on test1.asp(second page, the web address will
still show UserInterface.asp page as you know), click continue, on the third
page if they found something typed wrong, if they click back button in the
broswer, all data on the second page is gone. This only occurrs in IE,
Firefox is fine.
It's very annoying, how can I fix it, if not, is there any other way?
Thanks
--
Betty