Most of us use Firefox, except for a small number of people who attempt to work with a system called Windows.
Styles are not 100% compatible across all browsers, they all try their best, but not one is 100%
However as its a modified bluegreen.css I would suggest you restore the original and try again, its quite common for a newcomer to the heavy Tiki CSS files to change something and not realise its knock-on effects.
btw. Looks fine to me in Gentoo Linux, Firefox 1.5