Best Way to target CSS for Mac Firefox and Safari

I'm looking for the best way to target css specifically for Mac Firefox (2.0 and up) and Mac Safari. In looking around I'm seeing various ways and some that are dated and I'd like to know what people see as the most efficient. I'm a couple pixels off for one nav bar and the clients are all on macs.

thanks

The most efficient would be to write CSS so you don't need these kinds of hacks. The only semi-reliable way I can think of would be to use some sort of server-side script to test the user agent.