In the proposed design, the rarely called out actions like menu bar, home icon and status bar are removed which gives a clean and clear look for the browser ( as desired by user). The combo Stop/Refresh/Go button is the brilliant idea. By removing all the undesirable options, the actual web space is increased.

It proposes two primary designs: tabs-on-bottom (as in current firefox) and tabs-on-top (which resemble Google Chrome). The tabs-on-top version hides the title bar which has less importance among the net users. Anyway it is better to offer both the designs with an option for users to choose between the two as some users may need to have tabs in close proximity while others need to access the menu items quickly.

It has summarized the pros and cons of the two designs in its wiki as:

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 that confuse 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.

As a Firefox lover, I am looking forward for the release of Firefox 4.0 with a brand new design and exciting features.