I have some remote boxes, which are a bunch of Mac Mini's. I access them now through SSH, and it fits my needs to do the maintenance. In the past, I used X11Forwarding with Linux boxes, when I was still using Debian myself, and I was able to run a specific application as if it was natively present (Firefox). I haven't succeeded to do this yet, but I assume because of the BSD underneath the fancy Apple GUI should be able to do such a task similar. I am aware of the remote administration, but I rather keep access limited to SSH on these boxes for inbound connections. I use Leopard myself, so I connect from Mac-to-Mac.
Background information about the why's, tips, advice and comments are all helpful! Thanks!
You can't use native OSX Firefox (or any other normal MacOS program) via X11 forwarding because it's not an X11 application, but uses the MacOS graphics system instead.
If you want to use X11 aware programs, you'll need to install either MacPorts or Fink and then install the applications from there.
Some background: MacOS X uses Aqua as it's graphics system, which is not network aware. On Linux/Unix, you use X11 as the graphics system, which was designed from the ground up to work over a network. You use this network access method when you do X11 forwarding via SSH. Naturally, most applications on the Mac are built to use the Aqua system for graphics output, so X11 forwarding doesn't work here. But MacPorts and Fink aim to supply a complete Unix stack on the Mac, including the necessary X11 libraries and programs using them. You can display those locally on the Mac with the X11.app utilitiy Apple provides, or you can forward their display to another computer running X11.