Lifehacker has just pointed out that Mozilla has released some initial brainstorms of the design for Firefox 3.7 and Firefox 4.0.
It looks like they are going in the direction of creating a simplistic interface following the path of Google Chrome and Safari. Hiding the menu bar by default and using the two buttons (XP) on the right side. They also seem to be following Safari 4.0 changing colors with the Windows theme. See this. Notice that the toolbar color changes with the Windows theme color. On Vista, its just a tools menu with the page menu on the tab bar left instead.
This design also features (for Windows Vista/7) a full glass interface.
The current design for Firefox 4.0 features the Omnibar and Top Tabs.