1e928c53_nsIChannel___Mozilla___MDN__2
[0] notificationCallbacks [1] nsIInterfaceRequestor [2] 
The notification callbacks for the channel. This is set by clients, who wish to provide a means to receive progress, status and protocol-specific notifications. If this value is null, the channel implementation may use the notification callbacks from its load group. The channel may also query the notification callbacks from its load group if its notification callbacks do not supply the requested interface. Interfaces commonly requested include: nsIProgressEventSink, nsIPrompt, and nsIAuthPrompt / nsIAuthPrompt2. When the channel is done, it must not continue holding references to this object. Note: A channel implementation should take care when "caching" an interface pointer queried from its notification callbacks. If the notification callbacks are changed, then a cached interface pointer may become invalid and may therefore need to be re-queried.
nsIChannel - Mozilla | MDN