Hi, looks like a trick, but works... patch might be outdated, but the idea is here.
Created attachment 71223 [details] WebP->BMP->CG transfer
This is an ugly hack. I think a better approach is to switch over to using the WebKit image decoders entirely rather than creating a fake BMP. That approach seems to be making progress, so I'm closing this bug. Free free to re-open if that effort stalls.