Well, the XPCOMs represent the bytecode in your opinion. One still can't get an XPCOM for FF to work on FFoS, I meant the simplest one without making huge chang

Well, the XPCOMs represent the bytecode in your opinion. One still can't get an XPCOM for FF to work on FFoS, I meant the simplest one without making huge changes to the code base. Yes, one UI engine is needed and so is a (cross-)compiler in your case OR alteration of the code base for FFoS of FF to ensure portability. I guess it would be the FFoS code base that might need to change. BUt that could be tricky since it leverages the Andriod's core - a component-based linux OS.