Versions of the upcoming Firefox 12 in the nightly build phase have shown major changes coming to its interface. New tabs can now open to a hybrid portal page that mixes in features seen in Chrome and Safari. Along with seeing the most frequently visited sites and a search bar, it now has top web apps, the most recently shared apps, and a Google Talk status section to launch directly into chat.
The address bar now also has autocompletion for addresses in history or bookmarks. It should eventually come to the tab page, although this might not make the initial 12.0 release.
Seeing the full portal requires going into the advanced configuration pages. There's also no guarantee that every nightly build and OS variant will have the feature exposed.
If Mozilla keeps to its fast-track schedule of version releases, it should have a finished version of Firefox 12 in April, with version 11 arriving in between.