Boot to Gecko is an experimental Mobile Operating System by the Mozilla Foundation. Based off the Gecko Layout Engine, Coded in almost entirely HTML5 (easily mod-able) If you would like more information, you can read about it here For developers, modders, etc you can take a look at the source code here [video=youtube;hG6vPWSRtJo]https://www.youtube.com/watch?v=hG6vPWSRtJo&feature=player_embedded[/video] I must admit it looks pretty clean, it will be interesting to see where this goes. Screenshot source: XDA
You will need root and an unlocked bootloader on your phone. The source code for it is here: https://github.com/andreasgal/B2G If you have a Samsung Galaxy S 2 someone has started work on porting it here: [PRE-ALPHA] Mozilla Boot-To-Gecko (B2G) - NOT ANDROID, SOMETHING DIFFERENT - xda-developers, any other phone i guess you will have to see if anyone starts work on getting it up and running.