A forum member hackerman1 recently asked if it was possible for the address bar or the One Box, to have it´s own row in IE9 and later, in order to make more space for the open tabs.
The tab cum address bar does look cluttered when you have many tabs open.
The best possible solution at the moment seems to be to uncheck the ‘lock the toolbars’ option , and resize the One Box or the address bar, by grabbing the edge and dragging it with your mouse.
Now check the ‘Lock the toolbars’ option.
This should offer some more room for your tabs in Internet Explorer 9.
A small but useful tip! Thanks nithinr6.