ear, ear! porting OWB was a huge task while porting FF was/is trivial?
eh, eh, eh ... you guys never cease to amaze me! :-/
Well, maybe you should ask yourself why?
The FireFox GUI is entirely built on the XUL layer, so it's indeed much less work to port FireFox. You "just" implement the os-dependant layers like thread/mutex, memory, filesystem, network, input events, windowing system, ... (noone said this work was easy, but the very same work was also done with WebKit/OWB), and then everything above it is for "free", unlike WebKit/OWB where the whole GUI had to be implemented on top of the WebKit framework. But the drawback of the FireFox approach is that you also get a quite alien GUI with embedded menus and so on, not in a very amigaish style (though you can skin FireFox fortunately, but not everything can be done to mimic the original AmigaOS GUI).
So I have no problem saying porting FireFox is less work.
In fact, my guess is most of the work in FireFox/Timberwolf went into having a hardware/accelerated Cairo (to get a descent performance, since everything relies on it) and fighting against some details like event propagation through windows in XUL (clashing with AmigaOS design), and possibly some network stack issues (like thread safety for DNS resolution).