I try to prevent the Browser from using the :hover effect of the CSS.

$("ul#mainFilter a").hover(
     function(o){ o.preventDefault(); ...do my stuff... }, 
     function(o){ o.preventDefault(); ...do my stuff... });

I tired it with return false; to but it does not work. Does anyone know how to do this?

due the answers i give you some more nfo: I have set the a and a:hover styles, in my CSS already. Now if JS is available on the clients machine, i want to overwrite the effect with a smoother one. (using jQuery color plugin)

As mentioned by fudgey, a work around would be to set the style (using .css()) but i would have to overwrite every single effect specified in the CSS (see here: http://jsfiddle.net/raPeX/1/ ). I am looking for a generic solution.