Seemingly Mozilla is not happy about this, and decides to gain some users on Android smartphones by moving to Android's native user interface (ditching XUL technology which has been used for ages). Mozilla hopes that with a native Android interface, Firefox should start-up faster, and uses less memory and provides smoother zooming and panning. They also went as far as claiming such move would save battery power.
In other words, only the user interface will change (from XUL to native), but underlying engine is still the same Gecko. Mozilla oversees the benefits over the disadvantages (difficult for add-on builders, and difficult for localising into other languages)
Sources:
https://groups.google.com/forum/#!topic ... 42Jv6KDg7s
and New Firefox interface to speed up Firefox on Android (CNet)
UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.23) Gecko/20110920 AlexaToolbar/alxf-2.14 Firefox/3.6.23
