Fix #1405, don't give an error on about:home (which has a chrome: favicon)
Fix #1405, don't give an error on about:home (which has a chrome: favicon)

fzzzy/pageshot,fzzzy/pageshot,mozilla-services/pageshot,mozilla-services/pageshot,fzzzy/pageshot,fzzzy/pageshot,mozilla-services/screenshots,mozilla-services/screenshots,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/pageshot