On a "religious" note, we shouldn't be using CSS to target any browser. Unfortunately due to IE being waaaay behind on supporting CSS features (and all the bugs) hacks have been applied to target CSS for a given browser.
The Conditional Comments that IE uses... although ugly... do provide a handy mechanism for targeting a browser (and version)... I almost wish other browsers supported this.
I've seen a few sites do this... which is an interesting approach to handling targeting of various browsers.
<head>
<style>
body.safari form input{
/*special styles for Safari*/
}
body.firefox form input{
/*special styles for Firefox*/
}
body.firefox.v3-5 form input{
/*special styles for Firefox 3.5*/
}
</style>
</head>
<body>
<script>
//run code here, that sets the class and or id attribute on the body tag...
</script>
In the long run, they are all hacks... it just depends what kind of hacks you're willing to live with ;-)