The developers tried as they could.
Porting Firefox is very difficult, and there are not enough developers, so it's unlikely, I would even say that under current conditions - it's impossible. But there is Netsurf. NetSurf will save the world.
Personally, I believe that Firefox is not needed in KolibriOS, because it is very slow and hulking, and if a miracle happens and Firefox will be ported, KolibriOS will become unnecessary, because it will not be better than Windows, GNU/Linux or FreeBSD. I do not want another clone. KolibriOS must have its own Internet browser, same fast and lightweight like KolibriOS.
The Glass is Always Half Full!