One of the next versions of Firefox, Firefox 12, may feature a series of new interface elements and functionalities that should both appeal to OS X Lion users and introduce new navigation options for those who dont' want to save their-most accessed websites in a bookmarks bar anymore. As first noted by ExtremeTech, an early version of a proposed new tab page design snuck into a nightly version of Firefox; per Mozilla's multiple channel releases, users of Firefox can test different versions of the browser, which range from Nightly to Aurora, Beta, Stable, and those uploaded directly to Mozilla's FTP servers.
ExtremeTech wrote about the new tab page:
The Firefox home tab is a lot more exciting. Basically there are two phases: The first phase will add “launchers” at the bottom — one-click links to your downloads, settings, apps, and so on (pictured right). Phase two is a complete reworking of the home page paradigm, weaving in favorite apps, recent websites, and even instant messaging (pictured below). Phase one is expected to roll out with Firefox 12, but at the time of writing the code still hasn’t been committed.
However, as also noted in an update to the original post, it appears Mozilla has pulled the functionality from the Nightly release of Firefox, leaving it in the "UX version" available for download on Mozilla's servers. Upon comparing the standard Nightly build to the UX one, I noticed the latter already contains the grid design for top websites pictured above, and full-screen support for Lion.
I wasn't able to activate ExtremeTech's home tab page design with search, Top Apps, Top Sites and Chat in a single window; the current Firefox UX Nightly build features shortcuts along the bottom of the window to open History, Settings, Add-ons, Apps, and Downloads. A new "Restore Previous Session" button is also provided in case you haven't set Firefox to automatically re-open previously open tabs on launch.
Changes that appear in Firefox Nightly builds typically carry over to the other stages of development and are further tweaked with refinements and bug fixes, but there could be changes in the features that Mozilla decides to implement once version 12 hits the beta channel. As for Lion support, Mozilla failed to deliver any significant optimization since the OS' release back in July, unlike competitor Chrome which added new scrolling, full-screen support and gesture navigation (among other things) fairly quickly. A designer at Mozilla mocked up some ideas that the company could deliver in a future version of Firefox for Lion, but as of version 12 nightly (Firefox stable is currently at version 9) it seems those ideas haven't been taken into consideration yet.