It's the little things that count.
While Firefox 3.7 will bring with it some really cool hardware acceleration features, the next big, big build will be Firefox 4.0. Right now the designers are debating whether to keep the tabs on the bottom of the address bar, like it's done for Internet Explorer and Safari, or move tabs on top of the address bar, like Chrome and Opera do it.
Check out all the points for and against it in the video below. It's fascinating stuff if you spend as much of your day in the browser as we do.