For a while I was checking upcoming OS X releases for CAC compatibility. At least on OS X, it's surprisingly easy to get set up, with the hardest step finding a compatible card reader. Once you have that, you usually have to install a PKCS#11 module (usually CACKey for DoD). Once that's all done, it's presented as an additional Keychain for the rest of the system to use. I know Chrome and Safari work with it without further fiddling, and I'm pretty sure Firefox will as well.