Add the client certificate in the browser.
            Firefox supports the import of PKCS12 keystore. So, you are going to
                            "transform" the JKS keystore into a PKCS12 keystore:
            
               keytool -importkeystore -srckeystore clientKeystore.jks -srcstoretype JKS -destkeystore client.pfx -deststoretype PKCS12
Enter destination keystore password:
Re-enter new password:
Enter source keystore password:
Entry for alias clientkey successfully imported.
Import command completed: 1 entries successfully imported, 0 entries failed or cancelled
 
             
            Now, you can import the client certificate in Firefox. To do so, in
                            the Tools menu, click the Options entry, and click on the Advanced tab.
            You can go in Certificates tab and
                            click on View Certificates
                            button.
            In the Your Certificates tab, you can
                            click on the Import... button and
                            choose the client.pfx keystore file.