<script language="JavaScript" type="text/JavaScript">
//<![CDATA[
var min=8;
var max=18;
function increaseFontSize() {

var p = document.getElementsByTagName('p');
for(i=0;i<p.length;i++) {

if(p[i].style.fontSize) {
var s = parseInt(p[i].style.fontSize.replace("px",""));
} else {

var s = 12;
}
if(s!=max) {

s += 1;
}
p[i].style.fontSize = s+"px"

}
}
function decreaseFontSize() {
var p = document.getElementsByTagName('p');
for(i=0;i<p.length;i++) {

if(p[i].style.fontSize) {
var s = parseInt(p[i].style.fontSize.replace("px",""));
} else {

var s = 12;
}
if(s!=min) {

s -= 1;
}
p[i].style.fontSize = s+"px"

}
}
//]]>
</script>

<a href="javascript:decreaseFontSize();">-</a>
<a href="javascript:increaseFontSize();">+</a>