There is no ref in the first link so it should not work in another browser. I can test in IE because it doesn't work well in my PC.......
(Update) well, I risked it and tried it in IE. I will have to restart the PC after this
In IE 7 it doesn't display well either. I see Home Page twice, and the second link has extra space from the rest. So I would not just categorize it as a problem with Firefox. I wil try at home where I have IE 6. The problem might be on the server side. You might have problem with the Include and some of the css might not download correctly. Do you know if the server runs apache or IIS?
I suggest that you quicly write another page with a demo link menu, and test that one and see what happens. Then if you have a demo page, and care to attach the files, I could try it in Apache and IIS and see if I can notice difference in the serving of the pages.