Falling Snow tutorial - amending

Hi !
I used Kirupa’s excellent falling snow titorial, but cannot figure out one thing :
I want the falling snow to work within a masked area ( imagine a snowglobe , and the snow only inside it ) .
Whatever I seem to do , it insists on snowing everywhere :slight_smile: .

second issue - I inserted the falling snow at frame x in my movie, as thats when i want it to start ‘snowing’ in my snowglobe.
It works fine at first viewing , the snow kicks in on cue.
But i hit the ‘replay’ button my movie , the snow starts at the beginning of the scene , not at the frame i specified .

Any solutions ?
Ciao, wonkat