Linux clients signing in to VPN tunneling via Mozilla Firefox must ensure that the OpenSSL libraries are installed on the client. Most Linux versions come pre-packaged with OpenSSL. If you encounter a Linux user that does not have the required OpenSSL libraries, you can direct them to the following resource where they can be obtained and installed for free:
See http://www.openssl.org/related/binaries.html for details. (You can also advise users to compile their own version by directing them to the source at http://www.openssl.org/source/.) The required version is libssl.so.0.9.6b.