We've been though this before.
I use Firefox for banking, what you need is an 'add-on' called IE Tab
1.5. ( The banks know I use it but I have not told them how! Because
they say they do not 'support' Firefox )
Go to FF 'tools' click on 'add-on' and search. Once you've installed
it, Under IE Tab options add your secure site to 'Enable site filter'
This way the site thinks you are using IE, but you do not suffer the
lack of security of IE.