ear, ear! porting OWB was a huge task while porting FF was/is trivial?
That depends on the quality of the port. If you add a few ifdefs and type "make" and you get an alien thingie that doesn't use Amiga UI, doesn't use Amiga libraries, doesn't use Amiga locale, is slow etcetera... you'll get a poor port.
Examples of poorly done ports:
OS4 OWB ports (specially the first ones that relied on SDL)
Firefox for OS4
Examples of excellent ports:
Netsurf for OS4
Odissey for MorphOS
ATM Odissey runs rings around all existing Amiga browsers so you can safely say that porting it took much more work than porting Firefox.
BTW coder skills also affect the quality of the port and Fab is a great coder and his products are great too (MPlayer, Odissey...). His two most famous ports are probably the best ports done to any platform.