After a short (!) and desperate wait for Fire 3.X Android, we have nothing but a fork of it, called Firenzina, compiled for our Android devices, at last.
It always makes me feel good to see stronger engines coming to the stage one by one. I didn't fully tested yet Firenzina but i can tell it works with Chess for Android, although the loading phase may a little bit slow at the first time, followed by "fire.cfg not found" error. But it works without this file if you wait patiently.
In case you want it to challenge other engines, no problem. I have already set up some games vs the weak internal engine of CfA and everything went fluently in tournament mode as well.
You may download v2.4.1 of Firenzina at http://firenzina.wikispaces.com/
Additional info Aug,28th:
* It's possible to generate a fire.cfg file using "default" command in the console mode of Firenzina 2.4.2 under Windows and transfer the generated file to Android. Chess for Android installs it in the same folder as the engine. I didn't check yet if the parameters are used by the engine but will do that too.
* Firenzina looks very strong after a quick set of bullet games vs Critter 1.6a (lost 4-6 but competes well) and Black Mamba 2.0 (wins 6-4!). It seems the level of Firenzina is between Critter and Mamba.
Additional info Aug,29th:
* Fire.cfg works under Android. So, the engine parameters can be altered by editing the file before installing. I confirm that the hash size setting of the GUI overrides the setting in the config file.