nsIDOMEvent
nseventptr getinternalnsevent(); violates the xpcom interface guidelines boolean getpreventdefault(); deprecated since gecko 16.0 void initevent(in domstring eventtypearg, in boolean canbubblearg, in boolean cancelablearg); boolean isdispatchstopped(); violates the xpcom interface guidelines void preventbubble(); obsolete since gecko 24 void preventcapture(); obsolete since gecko 24 void preventdefault(); void serialize(in ipcmessageptr amsg, in boolean aserializeinterfacetype); violates the xpcom interface guidelines void settarget(in nsidomeventtarget atarget); native code only!
... preventcapture() note: use stoppropagation() instead.
... void preventcapture(); parameters none.

CustomEvent - Web APIs
(prevents the event from bubbling.) event.preventcapture() obsolete since gecko 24 obsolete; use event.stoppropagation instead.

Event - Web APIs
event.preventcapture() prevents the event from bubbling.