--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -208,16 +208,21 @@ DOMInterfaces = {
     'nativeType': 'nsDOMCaretPosition',
 },
 
 'CharacterData': {
     'nativeType': 'nsGenericDOMDataNode',
     'concrete': False
 },
 
+'ChromeWindow': {
+    'concrete': False,
+    'register': False,
+},
+
 'ChromeWorker': {
     'headerFile': 'mozilla/dom/WorkerPrivate.h',
     'nativeType': 'mozilla::dom::workers::ChromeWorkerPrivate',
 },
 
 'DOMRectList': {
     'headerFile': 'mozilla/dom/DOMRect.h',
     'resultNotAddRefed': [ 'item' ]
@@ -1489,16 +1494,18 @@ DOMInterfaces = {
 
 'WheelEvent': {
     'headerFile': 'DOMWheelEvent.h',
     'nativeType': 'mozilla::dom::DOMWheelEvent',
 },
 
 'Window': {
     'nativeType': 'nsGlobalWindow',
+    # When turning on Window, remember to drop the "'register': False"
+    # from ChromeWindow.
     'hasXPConnectImpls': True,
     'register': False,
     'implicitJSContext': [ 'setInterval', 'setTimeout' ],
     'binaryNames': {
         'postMessage': 'postMessageMoz',
     },
 },
 

--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -1281,25 +1281,29 @@ class CGClassHasInstanceHook(CGAbstractS
         hasInstanceCode = """
   const DOMClass* domClass = GetDOMClass(js::UncheckedUnwrap(instance));
   *bp = false;
   if (!domClass) {
     // Not a DOM object, so certainly not an instance of this interface
     return true;
   }
   """
+        if self.descriptor.interface.identifier.name == "ChromeWindow":
+            setBp = "*bp = UnwrapDOMObject<nsGlobalWindow>(js::UncheckedUnwrap(instance))->IsChromeWindow()"
+        else:
+            setBp = "*bp = true"
         # Sort interaces implementing self by name so we get stable output.
         for iface in sorted(self.descriptor.interface.interfacesImplementingSelf,
                             key=lambda iface: iface.identifier.name):
             hasInstanceCode += """
   if (domClass->mInterfaceChain[PrototypeTraits<prototypes::id::%s>::Depth] == prototypes::id::%s) {
-    *bp = true;
+    %s;
     return true;
   }
-""" % (iface.identifier.name, iface.identifier.name)
+""" % (iface.identifier.name, iface.identifier.name, setBp)
         hasInstanceCode += "  return true;"
         return header + hasInstanceCode;
 
 def isChromeOnly(m):
     return m.getExtendedAttribute("ChromeOnly")
 
 def getAvailableInTestFunc(obj):
     availableIn = obj.getExtendedAttribute("AvailableIn")

--- a/dom/webidl/Window.webidl
+++ b/dom/webidl/Window.webidl
@@ -334,8 +334,12 @@ partial interface Window {
   [Replaceable, Throws] readonly attribute object? content;
 
   [ChromeOnly, Throws] readonly attribute object? __content;
 };
 
 Window implements TouchEventHandlers;
 
 Window implements OnErrorEventHandlerForWindow;
+
+[ChromeOnly] interface ChromeWindow {};
+
+Window implements ChromeWindow;