I had to search quite a long time, the precise information is nowhere in the tutorials, so here it is.
How to have the Epass2003 recognized and the certificates it contains used under mozilla firefox and/or thundebird, using the feitian drivers :
You have to go to options/advanced/Security Devices.
In the window “Device Manager” click on “Load”.
In the window “Load PKCS #11 Device” click on “Browse”.
Go in “WINDOWS\system32”
select the file with the name “eps2003csp11.dll”
and click on “Open”.