what condition makes the nsiWebProgressListener.STATE_START being triggered in firefox?

According to https://developer.mozilla.org/en/nsIWebProgressListener

"This flag indicates the start of a request. This flag is set when a request is initiated. The request is complete when onStateChange() is called for the same request with the STATE_STOP flag set."

But it 开发者_如何学运维seems this is not being triggered on http gets of images. so what are the HTTP gets that trigger this event?

This sounds like https://bugzilla.mozilla.org/show_bug.cgi?id=600081. It seems like it should work for all HTTP gets, and it's just currently broken for images.