I love it. Firefox 4 is so damn fast. 2 quick observations:
1. The tabs were moved below the address bar, the ‘RSS Feed’ button was moved to the top of the Bookmarks menu, and the ‘Reload’ button was moved to the right end of the address bar. If you want these back right-click on a blank space on the menu bar or the tab bar (see how) and click ‘Tabs on Top’ to move the tabs below the address bar (see how), or select ‘Customize’ and drag the ‘Subscribe’ button to the address bar (see how), or select ‘Customize’ and move the ‘Reload’ button to the left of the address button (see how).
2. The Add-on toolbar isn’t on by default. To turn it on, right-click on a blank space on the menu bar or the tab bar again and click ‘Add-on bar’ or press the Control and slash buttons together (Ctrl+/) (see add-on bar).