Mozilla has announced they will be moving away from using XUL (eXtensible User interface Language, an XML grammar used by Mozilla to define user interfaces for Firefox and Thunderbird) in favor of using Android’s own Native user interface. The main reasoning behind this will be to improve Firefox’s performance on Android devices, which unlike your typical desktop/laptop PC, don’t have as much memory or processing power. By switching to the Android UI, Firefox users should see faster start-up and less memory (Firefox has gotten a bad reputation in the past for being a memory hog with the desktop versions) consumption. I should add at this time, it is only Android based phones that Mozilla will be making this change for, though it may include Tablets in the future.
At this time an exact Firefox version for this change to take effect has not been announced. Given Firefox 8 and 9 for Android are already in Beta and Aurora, the earliest we will see this change would likely be with Firefox 10 for Android due for release on January 31st, 2012. We will post more information on this in the future.
Source: Mozilla Links