I already use overflow: hidden style to hide the scrollbar for the tabs that I add manually, but when I am using the addTab function as per your example:
function addTab(){
index++;
$('#tt').tabs('add',{
title:'New Tab ' + index,
content:'Tab Body ' + index,
iconCls:'icon-save',
closable:true
});
}
The div that is added by your Javascript does not have the overflow: hidden style, so I would need to modify your Javascript that writes the div to add it (or the css that is uses, but tried that already and that does not do it).
Since it only does this with HTML5, there must be something minor that needs to be adjusted in your code to make it work.