Use two argument KURL ctor, the single argument ctor expects its input to be the output of a previous KURL::parse call, which is not the case here.
Created attachment 28489 [details] twoargctor.patch
Comment on attachment 28489 [details] twoargctor.patch r=me I wish ResourceResponse::setUrl() didn't use incorrect case (should be setURL)!
Landed in r41618, will fix the setUrl thing now.