We appreciate your interest in our design experiments!
The UI mock-ups shown on these pages were part of a meeting, and were for discussion purposes, and to explore different design directions. Some of them are already out of date.
Mozilla works in the open, and the way to get the latest in UI improvements to Firefox is to download the UX channel build for your OS, which will auto-update every night with various design experiments we're looking at.
Much ♥, Firefox UX Team.