This was split off from bug 1123518. The thumbnails were considered a hard P1 requirement, but I don't think we specifically discussed favicons. Whether we do this ends up affecting whether we want bug 573638 and bug 1089559 for the ReadingList.
For v1 I think we decided this wasn't a hard requirement and looks like a bit of work. I'd like to get this done because I think it adds a lot and helps with the fallback for when images aren't present but definitely not a hard requirement.