Observed result:
The fullscreen setting of exported manifest.webapp
should be "fullscreen": "true",
not "fullscreen": true
See here:
https://developer.mozilla.org/en-US/Apps/Developing/Manifest
Or you can't upload the app to FFOS Market.
Construct 2 version:
r149
By the way, unlike the FFOS tutorial,
the portrait/landscape setting
is on the properties settings of project now.