14 DAY TRIAL // Mozilla has been working on a new tab page for ages now, slowly evolving the feature. But it has done it in the separate UX branch, created by the Mozilla user experience team to test out ideas and design.
The UX branch is separate from the main Firefox branches as well as from the regular release and build cycle. It is based on recent Nightly builds, but it adds its own modifications and customizations.
One of the features that, the few, Firefox UX users have been enjoying (that's debatable) is a new tab page, in the vein of Chrome or Opera's.
A few months back, the new tab page, while functional, wasn't anything to lust over, it was basic in every sense. It maintained a list of recently visited sites, which you could customize, as well as bookmarks you wanted to be displayed in the new tab page and that was about it.
Since then, the page has gotten some polish; it looks better and is easier/more fun to use thanks to a few usability enhancements. However, it is now only limited to a 3x3 grid of your most visited sites.
You can pin your favorite sites, so that they don't get removed even if you don't visit them as often, as well as remove the sites that maybe you're not supposed to be visiting so often. Thumbnails are generated for the most popular sites, though this feature doesn't always work.
But that's about it, the new tab page is as basic as it gets. It's a visual improvement over previous iterations, but only marginally so. The feature gained a bit of interest since it temporarily showed up in the regular Firefox 12 builds. However, it was soon removed and it doesn't look like it will be added back too soon.