Unfortunately, the railroad overlay on this map does not work with Firefox 2.0.0.2.
The Firefox Error Console reports, among other things, that the browser does not support SVG or VML.
That's not entirely correct, at least as far as SVG is concerned, but apparently you have used some SVG codes that Firefox still does not recognize.
In addition, the Error Console reports some problems in your .css files.
Most, if not all, of the problems are well beyond my knowledge of web programming, so I cannot be of much assistance in fixing the problems.
About all I could do, should you want me to, would be to send you the information from the Error Console and the relevant Firefox SVG page from the Mozilla Developer Center.