The detail "YAHOO!" does not interfere with the tab labels, which is very good. The gray background is a nice change from the default Firefox Pink. The gray background is paired with black labels (tab, menu) for good detail from the first tab on the left to the last tab on the right, with no interference to any tab label.

Lose a couple of stars because a little bit of background image would be nice. A little color, keep the simplicity, keep the good contrast with the labels, keep no-interference with the labels.

quite a boring persona I have to say....