Johnathan Nightingale, Sr. Director of Firefox Engineering has posted on the Future of Firefox blog describing what is involved in switching Firefox for Android UI from XML to the new Native UI. While the rapid release process from a features stand point makes sense and works, this is not the case for this change over.
However, when we decided to rebuild Firefox for Android using a native UI, we recognized that the first release couldn’t ride the trains. The iterative release model that serves us so well with Firefox works best when most changes are incremental and independent. Building a new high-performance front end for Firefox on Android, by contrast, involves many interconnected pieces being rebuilt in tandem.
As a result the move over to the Beta channel may not align with that of the Firefox for desktop (January 31st, 2012) as the developers want to ensure that everything is working and are happy with the quality of performance. In the future, once this process has been successfully completed and working as promised, Firefox for Android release will follow the same release schedule as the desktop builds. If you are wanting to try out the new Native UI, it is on the Firefox 11 Aurora for Android build.