Very very quick demo of B2G followed by a quick hack of the homescreen:

You can find the code of the UI of B2g (gaia) on github. Reminder:

What is Boot To Gecko:

• An Operating System;
• Linux Kernel + drivers from Android (so B2G can run on most of the phones that are capable of running Android). Works on ARMv7, will probably work on ARMv6;
• Gecko on top of it. The same version you'll find on a regular Firefox;
• Apps are written in HTML, JavaScript and CSS;
• You don't need to be online to use the Apps;
• A set of new JavaScript APIs:
  • WebAPIs, for bluetooth, sms, telephony, …
  • WebRTC, for streaming, webcam, P2P, …
• We are working on standardizing these APIs;
• The homescreen/launcher is an HTML page. Mozilla's version is named Gaia;
• You can build your own homescreen/launcher;
• The name of the project will probably change;
• It's possible to implement Boot To Webkit too;
• It's Open Source;
• We (Mozilla) are working on a MarketPlace.