Horizontal Drop Down Menus in CSS

I recently added horizontal drop menus to the Portage Park District website (www.portageparkdistrict.org). CSS drop-downs take advantage of unordered lists, which they supplant by applying styles and using opacity to create visual effects. During the process two key CSS rules were reinforced:

CSS does not act across frames.
Get rid of your frames or they will cut off your css display! The previous web administrator had an unnatural fondness for frames. I eliminated frames across more than fifty pages on the site, and eliminated the button javascript, freeing up more horizontal space on the pages as well!

Internet Explorer will interpret your CSS differently from Firefox.
Where Firefox uses the CSS standard and displays CSS beautifully, IE will require some tweaks and adjustments. There goes Microsoft again, trying to be different. Are they steering us toward their proprietary solution? Looks fine in Firefox? You are going to have to test in IE over and over again!