the code for the oder email binding (which you say is working) uses the CheckoutWizard_Basic_Default form:
WA_getSavedFormValue("CheckoutWizard_Basic_Default","Email_Address")
The code for the OrderBillFirstName is using a diferant form, CheckoutWizard_NewFromBlank_Default,:
WA_getSavedFormValue("CheckoutWizard_NewFromBlank_Default","First_Name"))
go through each of the bindings and make sure they are all using the same form binding, CheckoutWizard_Basic_Default