opacity?

[Fr�d�ric De Vries]

I can't get the opacity property to work in Mozilla 0.9.1.
And the only documentation I can find is that the proper style property 
to use should be 'mozOpacity'. In one of the viewer demos I see a 
certain '-moz-opacity' property in the source. But neither of these 
work. And I have no clue wether the value should be relative or absolute 
or whatever unit I should use.

Anybody out there who can give me some answers?