Sure about that?
There is still some manifestURLs in findmydevice:
  https://github.com/mozilla-b2g/gaia/blob/master/apps/findmydevice/manifest.webapp#L41
and platform code still check for manifestURLs attribute:
  http://mxr.mozilla.org/mozilla-central/source/dom/apps/src/InterAppCommService.jsm#306