I would add my site buttons A + and A-to zoom. I wish that all the body is grossise So I created this code
<html>
<body>
    <style>
    .container{width: 800px;background: #000;}
    p{color:#fff;}
    a { color: #FFCC00;}
    </style>
    <div class="container">
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dolorum, qui, sunt, totam quaerat repudiandae dignissimos maxime et perspiciatis aperiam doloremque eaque eum explicabo ullam deleniti sed adipisci obcaecati fuga similique.</p>
<script type="text/javascript">
function ZoomScreen100() {
document.body.style.zoom="100%"
 }
function ZoomScreen200() {
document.body.style.zoom="200%"
 } 
function ZoomScreen300() {
document.body.style.zoom="300%"
}
function ZoomScreen400() {
document.body.style.zoom="400%"
document.body.style.zoom="400%"
}
</script>
<a href="#" onclick="ZoomScreen100()">A+</a>
<a href="#" onclick="ZoomScreen200()">A+</a>
<a href="#" onclick="ZoomScreen300()">A+</a>
<a href="#" onclick="ZoomScreen400()">A+</a>
</body>
It works on Chrome, Internet Explorer, Safari but not on Firefox and Opera. Why?