You would have to look at the license and see if it's GPL/LGPL/MIT/etc, but I would assume absolutely not. At least not firefox, but you could use the code base and make your own browser based on Gecko/XUL and probably charge for it, except you would need to contribute back source modifications you make to the components. As far as one individual porting something like that, I say good luck.
Mozila is working on a mobile Firefox already, and I'm sure they'll be porting it to the iPhone very soon. I would see if you could officially contribute to their project.
Yeah, thanks
And of course this is on the assumption that Apple don't simply censor it on the grounds that "it could let viruses in or endanger the stability of the network" lol.
I would quite like to see ol' Foxy on the iPhone/Touch.