The ‘tabs on top’ idea that (I’m pretty sure) was first introduced in Opera, went to Chrome, and has made an appearance in the beta release of Safari 4 is a trend that I would like to see continue in the browser market. A tab is a visual clue that groups the content it is visually connected to. So I think it would make sense that a tab in a browser visually connects the address bar, search box, back button, and website that it is logically connected to.

Previously, browsers would often group the navigation elements with tabs and have the website floating below or have the website grouped in a tab with the navigation elements floating above. This shift marks a change in UI that I think just plain makes sense. Hopefully Firefox and IE aren’t far to follow in this trend.
