According to Nightingale, the native UI will allow Firefox to achieve better startup times, reduce memory consumption and become much more responsive. The mobile browser has been heavily criticized for its generous memory consumption and slow startup in the past.
Of course, this change will ring in another round of discussions that will center around add-on support. Nightingale said that the change to a native UI is still in its early days and there are talks with the Add-on SDK team how support extensions. While this could be another painful switch for developers, Mozilla stresses that its discussions are open and that it welcomes participation from the community.
There is no information when the new UI will be available. According to Nightingale, Firefox 8 and 9 will still ship with the XUL and tablet UI.