Right now the code for bug 172817 has to createInstance a webshell (and then use it without actually initing it, etc) just because it wants to use an nsIWebPageDescriptor to load data without rehitting the network). I feel that we should probably allow either passing nsIWebPageDescriptor to nsIWebBrowserPersist or passing it to the URILoader in some way (and getting back data?). Or both. Or something else that allows me to go from a web page descriptor to something useful... Thoughts?

We're going to delete this interface altogether in bug 1443355.