We have updated to 6.3R5 and this version resolves the problem. Firefox + IVE + DWA 8.0.1 work correctly.
Thanks to all for you help.
I upgraded to 6.3R5 and this has also fixed my Firefox and Safari issues with Domino.
I orginally went to 6.4R2 and although it fixed my problems, it introduced a new issue of single sign on no longer working. So I stuck with 6.3R5 for now.