This file contains various things we've found out while getting B2G working on various devices.
If you run a factory reset on the stock firmware, the restored /data/system directory receives the wrong permissions. This will cause the device to enter a boot loop. To fix this, adb shell into the phone (the boot loop doesn't effect adb), and change the /data/system directory permissions to 700. This should cause the phone to continue boot through to the GUI.