In https://searchfox.org/mozilla-central/source/netwerk/protocol/wyciwyg/PWyciwygChannel.ipdl the Init, AsyncOpen, and AppData methods take Principals, URIs, and SerializedLoadContext from the Content Process. A rogue Content Process could provide fraudulent values for these values. I've had difficulty tracking down what the exact impact of this could be. But it seems likely that these values need to be validated to ensure the values provided by the Content Process are permitted to come from this particular Content Process.