I'm creating on WindowsXP a Projector (DirectorMX 2004) both for
WindowsXP and Mac Classic (9). It contains a button with a "go to URL"
attached Behaviour. It works fine on WindowsXP, opening a browser
window which shows my local file "index.htm". But the Mac version
crashes as soon as I hit the button and prompts an Error#3. It seems,
Macs do not understand any URLs without "http://" at the beginning.

Is this so? What can be done?

(Everything else on my Projector goes pretty well on the Mac. So maybe
it's not a question about authoring for Mac on the Mac, is it?)