The code in the common.js javascript library for the function 'quote(mode)' only works in IE since FireFox doesn't use document.selection.
So I changed it to this so that it works in both IE and FireFox:
//quote parent
function quote(mode) {
if (mode!='')<br/>
{<br/>
var selectedText;<br/>
if(document.selection)<br/>
{<br/>
selectedText = document.selection ;//IE<br/>
if (selectedText.type=='Text')<br/>
{<br/>
var newRange = selectedText.createRange(); <br/>
tmp_text=newRange.text<br/>
}<br/>
else<br/>
{<br/>
return true<br/>
}<br/>
}<br/>
else<br/>
{<br/>
selectedText = window.getSelection() ;//FireFox<br/>
tmp_text = selectedText.toString();<br/>
}<br/>
}<br/>
else {var tmp_text=onimod_parenttext}<br/>
tmp_text=tmp_text.replace(new RegExp("(<BR>)", "g"),'\n')<br/>
document.forms[0].Content.focus();<br/>
document.forms[0].Content.value = document.forms[0].Content.value+'[QUOTE]'+tmp_text+'[/QUOTE]';<br/>
_UpdateContentPreview ()<br/>
}