I have perfectly installed MorphOS alongside with MacOSX, but as the guide mentions, it boots at MacOSX by default. What is the key combination to enter the firmware and what to type there in order for MorphOS to be the default OS? Command + Option + o + f keys doesn't seem to work for me.

What you need to type that is at the very end of that dualboot.pdf.

If your unable to enter OF, remove all hubs between KBD and Mac. If that doesn't help try a different KBD.

Edit:
Scrap that if your on the PowerBook, but might still be a problem with your KBD, try an external one.

[ Edited by Kronos 24.11.2013 - 17:49 ]

So, command + option (is next to command?) + o (letter key) + f (letter key) is the right combination?

Is there any alternative, to do it via MacOSX for example?

[ Edited by Phantom 24.11.2013 - 18:52 ]