In the light of the FREAK TLS vulnerability, how may I disable insecure cipher suites manually in Safari?
Safari on OS X uses Secure Transport for SSL/TLS, the same implementation which is linked in cURL, App Store, etc. Secure Transport does not have any user configurations available. Therefore, it is not possible to modify Safari cipher suites.

Anyway, Apple recently released Security Update 2015-002 which fixes this issue.


  Impact: An attacker with a privileged network position may intercept
  SSL/TLS connections
  
  Description: Secure Transport accepted short ephemeral RSA keys,
  usually used only in export-strength RSA cipher suites, on connections
  using full-strength RSA cipher suites. This issue, also known as
  FREAK, only affected connections to servers which support
  export-strength RSA cipher suites, and was addressed by removing
  support for ephemeral RSA keys.
  
  CVE-2015-1067 : Benjamin Beurdouche, Karthikeyan Bhargavan, Antoine
  Delignat-Lavaud, Alfredo Pironti, and Jean Karim Zinzindohoue of
  Prosecco at Inria Paris


You can examine Secure Transport client with something like, curl "https://www.howsmyssl.com/a/check" | tr ',' '\n'. As someone pointed out, it is also a good idea to use Firefox or Chrome which use NSS instead.