This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
settingValue property of the
MozSettingsEvent object returns the setting's new value.
var value = instanceOfMozSettingsEvent.settingValue;
Typically a string or number, this is the value of the affected setting.
Not part of any specification yet; however, this API will be discussed at W3C as part of the System Applications Working Group.