CSS Menu's & very inefficient rules per firebug

This maybe real simple. I have presently purchased Design suite and testing it for my website. I took a simple Eric Meyer's CSS sculpture 3 page and injected a stock standard horizontal menu. When I test on my test sever (seperate box unbuntu with Lamp server) page comes up ok, but when I use Firebug to check performance I get this.
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Use efficient CSS selectors

menu.css has 13 very inefficient rules, 3 inefficient rules, and 5 potentially inefficient uses of :hover out of 21 total rules.

What am I doing wrong?

due to the nature of creating cross browser CSS to ensure that the menus will function in IE, FireFox, Opera and Safari, some of the css rules may not pass through efficiency testing in FireBug, this is not to say that rules are wrong or somehow broken. They are needed to ensure that the menus function across all modern browsers.