And here's the tabs-on-top design:
In addition, Mozilla summarizes the pros and cons of the two designs very succinctly:
Positives:
- Save Vertical Space
- Efficiency/Remove Visual Complexity - Right now the tabs have to be connected to something. So we are adding an extra visual element for them to connect to.
- Shorter Mouse Distance to Page Controls
Negatives:
- Breaks Consistency/Familiarity - Moving things confuses existing users.
- Title is MIA - With the space removed from the titlebar you only get the truncated version in the tab.
- Longer Mouse Distance to Tabs - Takes longer to mouse to a tab.
- Lost Space - Sandwiched in between the application icon and the window widgets you lose some space.
While we won't go into detail on the debate, we will say this: if Mozilla can offer the ability to choose between the two designs, it should. Some users need to get to the menu items faster, while others prefer having the tabs in closer proximity.
New Firefox 4.0 Feature: Combo Stop/Refresh/Go Button
Firefox 4.0 incorporates all of the design changes featured in Firefox 3.7 and includes a few new features. The big one is a Combo Stop/Refresh/Go Button.
Instead of separate buttons for each of these functions, they're all integrated into one button on the right hand side of the address bar. It also changes colors based on your actions. So if you're typing, it will be a green "Go" button, but if the page is currently loading, a red "Stop" button will take its place. Not a bad way to save space, if we do say so ourselves. Here's a screenshot of the new feature in action:
