Firefox/4.0 Windows theme mockups posted at wiki.mozilla.org. The interfaces are not final, they just for brainstorming/exploration. More pictures after the jump
Version A – Tabs-on-Bottom
Possibly add a Bookmarks widget as an upfront replacement for the Bookmarks menu/Bookmarks toolbar (option to turn those on would remain).
Version B – Tabs-on-Top
The more contentious Tabs-on-Top concept.
* 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
* 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.
Combo Stop/Refresh/Go Button.
Attached at the end of the location bar.
* Turns green when you start typing.
* Blends with the location bar when at rest.
* Turns blue on hover.
* Turns red when a page is loading.
The proposed iconography is mostly colorless. Adding color to these temporary action driven buttons will make it more obvious something is going on.