nsIUUIDGenerator is implemented by a service that can generate
 universally unique identifiers, ideally using any platform-native
 method for generating UUIDs.
[scriptable, uuid(138ad1b2-c694-41cc-b201-333ce936d8b8)]
interface nsIUUIDGenerator : nsISupports

Methods

 Obtains a new UUID using appropriate platform-specific methods to
 obtain a nsID that can be considered to be globally unique.

 @returns an nsID filled in with a new UUID.

 @throws NS_ERROR_FAILURE if a UUID cannot be generated (e.g. if
 an underlying source of randomness is not available)
nsIDPtr generateUUID() 
 Obtain a new UUID like the generateUUID method, but place it in
 the provided nsID pointer instead of allocating a new nsID.

 @param id an existing nsID pointer where the UUID will be stored.

 @throws NS_ERROR_FAILURE if a UUID cannot be generated (e.g. if
 an underlying source of randomness is not available)
[noscript] void generateUUIDInPlace(in nsNonConstIDPtr id)