I know that using conditional comments will work of IE browsers (Except IE10), but i want to know how to do same in Firefox and chrome. 
Do i need to create different stylesheets for different browsers?
Please answer with a example of some small code, so i can get it well. 
NOTE: I m not that good at javascript, so if answer is using javascript, please make some simple script.
Here is my code:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <!--[if IE]>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
    <script src="http://css3-mediaqueries-js.googlecode.com/svn/trunk/css3-mediaqueries.js"></script>
    <link href="IEStyleSheet.css" rel="stylesheet" />
    <![endif]-->
</head>
<body>
        <div class="Container">
            <header>
            </header>
            <nav>
            </nav>
            <div class="content">
                <section class="main_articles">
                    <article class="siteDescription">
                        <div class="desImage">
                            
                        </div>
                        <div class="des">
                        </div>
                    </article>
                </section>
                <aside class="side_article">
                    <div class="ads">
                        This is a Advertisement.
                    </div>
                    <div class="ads">
                        This is a Advertisement.
                    </div>
                </aside>
            </div>
            <footer>
            </footer>
        </div>
</body>
</html>