I remember when Firefox 3 was released making a world record for most downloads in 24 hours, the guys at Mozilla had already started working on the next Firefox. I even got a glimpse of the Firefox 4 Alpha 1 from their FTP, but not sure if that was the official one.

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.