It appears that MAC OS 10.9 and above will have OS and browser support for TLS v1.2.
https://discussions.apple.com/thread/5128209?start=0&tstart=0
http://en.wikipedia.org/wiki/Transport_Layer_Security#TLS_1.2
Option 1
To download FotiClient v5.0.6, login to support.fortinet.com and click "Download" -> "Firmware Images" -> Select "FortiClient" in the drop down list. Then browse to v5.0.6 FCT download.
Option 2
The default FortiGate configuration is as follows for the TLS negotiation on v5.2.2 of the FortiOS. If you would like to keep the latest FCT software installed you can disable TLSv1-2 in the CLI on the FortiGate and the max negotiation that will occur with the FCT will be v1.1.
config vpn ssl settings set tlsv1-0 enable set tlsv1-1 enable set tlsv1-2 enable end
Let me know if this helps.
Best Regards,
-Robin.