I wonder if their closed-source components are the legal reason they have to call it Timberwolf instead of Firefox.
From the Timberwolf project page
There are no plans for any older version of AmigaOS nor for any other AmigaOS-alike system.
A shame, since AROS will run on much better and widely-available hardware, and MorphOS has the edge over OS4 in many areas.
I can see why 68k AmigaOS would be too slow though (other than under WinUAE etc.)