STR: 1. Place the phone side-says on a desk 2. Reboot the phone 3. Wait until the lock screen show up Expected: 1. Lock screen shown in portrait Actual: 1. Lock screen shown in landscape 2. Once you unlock the phone, the home screen will be in portrait 3. However, if one turn off the screen and turn on again, the lock screen will once shown in landscape. Note: We have dealt with similar thing in Gaia (bug 936253). Greg, Alive, could you quickly work together to verify if there isn't any more bugs in Gaia orientation handling? Viral, does this have anything to do with orientation: default? This bug is reproducible on Peak and Unagi.

Taken

The root cause is gecko doesn't give us the default orientation, but we could do this trick by lockOrientation on device booting to get the default orientation.

Alive and I discuss this issue for bug 934556. Now OrientationObserver will enable in nsAppShell and start to notify the sensor changes if we have any. So if there's no any app lock orientation, OrientationObserver will keep working. The way in my expect to lock in default orientation could be mozLockOrientation. by using manifest.webapp seems more complexity to me.

Comment on attachment 8341545 [details] https://github.com/mozilla-b2g/gaia/pull/14296 We could do that for now. Do you think it make sense to expose |screen.mozDefaultOrientation|? I thought we have that already.

No, we don't have the API yet.

Sounds like a regression, so that makes this a clear blocker.