This is how you enable smart cards in Mozilla Firefox (for the old Mozilla and Thunderbird it is mostly the same):
1.) Start Mozilla or Firefox or Thunderbird.
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox1.jpg?format=raw
2.) Select "Tools" on the menu bar, select "Option...".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox2.jpg?format=raw
3.) Select "Advanced" Options. Unfold the "Certificates" section. Click on "Manage Security Devices".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox3.jpg?format=raw
4.) Click on "Load"
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox4.jpg?format=raw
5.) Change the name to "OpenSC PKCS#11 Module". Click on "Browse."
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox5.jpg?format=raw
6.) Select the installation directory. On windows this is usualy "C:\Program Files\Smart card bundle". On Linux and Mac OS X choose "/usr/lib/". Click on "opensc-pkcs11.dll" (windows) or "opensc-pkcs11.so" (Linux, Mac OS X). Click "Open".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox6.jpg?format=raw
7.) Click "Ok".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox7.jpg?format=raw
8.) Click "Ok".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox8.jpg?format=raw
9.) Click "Ok".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox9.jpg?format=raw
10.) Click "Ok".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox10.jpg?format=raw
11.) Click "Ok".
http://www.opensc-project.org/opensc/attachment/wiki/MozillaSteps/firefox11.jpg?format=raw