关于这个问题，我的解决方案如下：

JAVASCRIPT部分：

var prefsLoaded = false;
var defaultFontSize =100;
var currentFontSize = defaultFontSize;

function revertStyles(){

currentFontSize = defaultFontSize;
changeFontSize(0);

}

function toggleColors(){
if(currentStyle == “White”){
setColor(”Black”);
}else{
setColor(”White”);
}
}

function changeFontSize(sizeDifference){
currentFontSize = parseInt(currentFontSize) + parseInt(sizeDifference * 5);

if(currentFontSize > 220){
currentFontSize = 220;
}else if(currentFontSize < 60){
currentFontSize = 60;
}

setFontSize(currentFontSize);
};

function setFontSize(fontSize){
var stObj = (document.getElementById) ? document.getElementById(’content_area’) : document.all(’content_area’);
document.body.style.fontSize = fontSize + ‘%’;

//alert (document.body.style.fontSize);
};

function createCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime()+(days*24*60*60*1000));
var expires = “; expires=”+date.toGMTString();
}
else expires = “”;
document.cookie = name+”=”+value+expires+”; path=/”;
};

function readCookie(name) {
var nameEQ = name + “=”;
var ca = document.cookie.split(’;');
for(var i=0;i < ca.length;i++) {
var c = ca[i];
while (c.charAt(0)==’ ‘) c = c.substring(1,c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
}
return null;
};

window.onload = setUserOptions;

function setUserOptions(){
if(!prefsLoaded){

cookie = readCookie(”fontSize”);
currentFontSize = cookie ? cookie : defaultFontSize;
setFontSize(currentFontSize);

prefsLoaded = true;
}

}

window.onunload = saveSettings;

function saveSettings()
{
createCookie(”fontSize”, currentFontSize, 365);
}

参考了Joomla developer本站的JS代码，有reset设置，并且设置记录到cookie下次留用。

HTML部分：

<h3><?php echo JText::_(’FONTSIZE’); ?></h3><p class=”fontsize”>
<a href=”index.php” title=”<?php echo JText::_(’Increase size’); ?>” onclick=”changeFontSize(2); return false;” class=”larger”><?php echo JText::_(’bigger’); ?></a><span class=”unseen”>&nbsp;</span>
<a href=”index.php” title=”<?php echo JText::_(’Decrease size’); ?>” onclick=”changeFontSize(-2); return false;” class=”smaller”><?php echo JText::_(’smaller’); ?></a><span class=”unseen”>&nbsp;</span>
<a href=”index.php” title=”<?php echo JText::_(’Revert styles to default’); ?>” onclick=”revertStyles(); return false;” class=”reset”><?php echo JText::_(’reset’); ?></a>