Just like there was a new interface in Firefox 3, the FF team is again working on a new and much-improved interface for Firefox 4.
Two mockup designs have been released on the Mozilla Wiki to gather user-feedback and improve their designs further. These two mockups show two versions, tabs on top and tabs on bottom on Windows Vista default theme.
Tabs on Top
A bookmarks menu has been added next to the address bar, also known as the Awesome Bar.
Tabs on Bottom
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.
* Chrome-ish - Looks more like Google Chrome, the first browser with tabs on top.