If there's a network error reported to imgRequest::OnStopRequest() it will throw away the existing (partially downloaded) image and instead render the "no image found" symbol. The current work for Bug 237623 intends to fix this behavior for the situation where a network transfer is detected "partial", but it seems we should expand the check and allow the code to keep a partial image to get shown for more (network) errors that can potentially happen. The effect is particularly disturbing if almost the entire picture has been downloaded and/or if the transfer is very slow. I suggest we expand the check added in Bug 237623 to also check for these errors and allow them to show partial images: NS_ERROR_NET_TIMEOUT NS_ERROR_NET_RESET NS_ERROR_NET_INTERRUPT