--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -32,20 +32,16 @@
 #                   .webidl file and the values are the names as they should be
 #                   in the WebIDL.
 #   * wrapperCache: True if this object is a wrapper cache.  Objects that are
 #                   not can only be returned from a limited set of methods,
 #                   cannot be prefable, and must ensure that they disallow
 #                   XPConnect wrapping.  Always false for callback interfaces.
 #                   Defaults to true for non-callback descriptors.
 #
-# A descriptor can have 'wantsXrays': False specified if it
-# should not have Xray hooks generated.  Make sure to have someone
-# familiar with Xrays review any use of this!
-#
 # The following fields are either a string, an array (defaults to an empty
 # array) or a dictionary with three possible keys (all, getterOnly and
 # setterOnly) each having such an array as the value
 #
 #   * implicitJSContext - attributes and methods specified in the .webidl file
 #                         that require a JSContext as the first argument
 #
 # The value for an interface is a dictionary which specifies the

--- a/dom/bindings/Configuration.py
+++ b/dom/bindings/Configuration.py
@@ -274,17 +274,17 @@ class Descriptor(DescriptorProvider):
     """
     Represents a single descriptor for an interface. See Bindings.conf.
     """
     def __init__(self, config, interface, desc):
         DescriptorProvider.__init__(self)
         self.config = config
         self.interface = interface
 
-        self.wantsXrays = desc.get('wantsXrays', True)
+        self.wantsXrays = interface.isExposedInWindow()
 
         # Read the desc, and fill in the relevant defaults.
         ifaceName = self.interface.identifier.name
         # For generated iterator interfaces for other iterable interfaces, we
         # just use IterableIterator as the native type, templated on the
         # nativeType of the iterable interface. That way we can have a
         # templated implementation for all the duplicated iterator
         # functionality.