Mozilla has build a new OS for mobile. It's open sourced and not Android. It's completely different from it. Till now it's in very early stage so not all the feature are working. Only few things floating good. For more details you can you can visit it office site. Click here to read more.
It's already been ported to Samsung Galaxy S II. You can have a look here.
If you really want o have it on Phone then you should follow this linkt
You can more details on XDA Portal.