“或'在PHP中,但它在浏览器中显示\”或\'

I fill " or ' at Input Text firstname and press submit, but the browser shows \" or \'. I want it to show only " or '. How I can do this?

<?php
    echo $_POST['firstname'];
?>
<html>
    <body>        
        <form method="post">
            <input type="text" name="firstname" placeholder="Firstname"/>
            <input type="submit" name="ok" value="OK" />
        </form>
    </body>

Thanks.

stripslashes(); is very simple for this problem.