Fix #1720, allow view-source URLs
Fix #1720, allow view-source URLs

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