The question is which browsers are known not to support Forward Secrecy and the Diffie-Hellman (DHE) or Elliptic Curve cryptography (ECDHE) ciphers? We have clients who are demanding we support forward secrecy for them to continue to use our products. We need to determine if it may have an affect on other clients which may not be on latest browsers. Are there any lists of known, or unknown support browsers. Our F5 will be setup to use Elliptic Curve cryptography (ECDHE) ciphers.
Most browsers (all the major ones) allow you to change the set of cipher suites in use. Some may require obscure ways to do this (I'm looking at you chrome) and others may depend upon the cryptography packages provided by the operating systems.
Chrome, Opera and Firefox support FS pretty well out of the box. IE and Safari will require some tweaking. Check out SSL Lab's list of user agent capabilities.
Forward secrecy involves the use of ephemeral keys which are not transmitted across the network. This assumes that neither side has been compromised. Qualys has a good overview of FS.