nsIMutable defines an interface to be implemented by objects which
 can be made immutable.
[scriptable, uuid(321578d0-03c1-4d95-8821-021ac612d18d)]
interface nsIMutable : nsISupports

Attributes

 Control whether or not this object can be modified.  If the flag is
 false, no modification is allowed.  Once the flag has been set to false,
 it cannot be reset back to true -- attempts to do so throw
 NS_ERROR_INVALID_ARG.
attribute boolean mutable