Just two weeks Mozilla developers showcased an upcoming UI designed for tablets and declared that Mozilla was working on a tablet version of Firefox. The tablet version of Firefox would run on Android-based tablets and be flexible enough to work in both portrait and landscape mode. You can learn more about the UI from our previous coverage.
Parts of this UI have already been implemented and are now available in the nightly channel of Firefox Mobile (which would be Firefox Mobile 9).
What you can already see is the thumbnail-based tabbed interface on the left (although tab thumbnails don't seem to be showing right now) and the drop-down menu on the right.
A version for Windows is available (as always) if you just wish to check out the application without affecting your device. If you download and launch the application on Windows right now you will notice that it shows the Mobile interface of Firefox. All you need to do is resize the window and when it crosses a certain threshold it will switch to the tablet UI automatically! The Windows version (at least) doesn't seem to support the portrait version right now, but this is just the beginning.
You can download the nightly version of Firefox for Mobile for your OS / device from here. Do know that the nightly versions of Firefox can be quite unstable, since they include a lot of code that is untested.