There is a better way, especially when you consider that css style is not javascript and should work even if javascript is disabled. You should set up your styles for FF in one file and link to it first in the head of your page, ex:
HTML Code:
<link rel="stylesheet" href="ff_styles.css" type="text/css">
These ff_styles.css rules will be used for all browsers. Then make up your styles for IE, overriding any of the styles in ff_styles.css if and where need be and including any additional styles that are for IE only. Link them next in the head like so:
HTML Code:
<!--[if IE]>
<link rel="stylesheet" href="ie_styles.css" type="text/css">
<![endif]-->
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