hi mariuss.

Of course, EXDATE or EXRULE is defined in RFC2445.
But implementing this is very complex.
(only RRULE is enough complex, but RRULE with EXRULE is far more complex...)

Perhaps, OutLook or iCal don't implement it.
I guess this is because implementation is too complex.

I respect the author of Mozilla Calendar.
He must be the super programmer.