connectionType property indicates for which network the data usage statistics are provided.
The value for this property is the same as the one provided within the option parameter of the
MozNetworkStatsManager.getNetworkStats() method. If this property is
null, it means that the data usage statistics are a merge of the data from all networks.
var type = instanceOfMozNetworkStats.connectionType;
A string or
Not part of any specification.