How can I install the X11 version of Firefox on Snow Leopard? (Preferably without MacPorts or Fink?)

I’m doing some screen-scraping using Selenium, a framework which lets you programmatically control web browsers on your system. I’m running it as part of a web app on a Linux server, and on my MacBook Pro for when I’m writing the web app. On my server, Selenium uses Firefox headlessly (by using Xvfb instead of a real display). I’d like to do the same thing locally, so that I don’t have Firefox windows popping up all the time whilst I’m writing and testing Selenium code. In order to do this, I need to install the X11 version of Firefox on my Mac. I’ve seen a lot of references to MacPorts and Fink, but is there a way to just install the X11 version of Firefox, rather than installing MacPorts or Fink just for this one-off?