diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index bf21e3ebbb52..1a13488f795d 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -78,9 +78,7 @@ def idlTypeNeedsCycleCollection(type):
 
 
 def wantsAddProperty(desc):
-    return (desc.concrete and
-            desc.wrapperCache and
-            not desc.interface.getExtendedAttribute("Global"))
+    return (desc.concrete and desc.wrapperCache and not desc.isGlobal())
 
 
 # We'll want to insert the indent at the beginnings of lines, but we
@@ -372,7 +370,7 @@ class CGDOMJSClass(CGThing):
 JS_NULL_CLASS_EXT,
 JS_NULL_OBJECT_OPS
 """
-        if self.descriptor.interface.getExtendedAttribute("Global"):
+        if self.descriptor.isGlobal():
             classFlags += "JSCLASS_DOM_GLOBAL | JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(DOM_GLOBAL_SLOTS) | JSCLASS_IMPLEMENTS_BARRIERS"
             traceHook = "JS_GlobalObjectTraceHook"
             reservedSlots = "JSCLASS_GLOBAL_APPLICATION_SLOTS"
@@ -415,7 +413,7 @@ JS_NULL_OBJECT_OPS
             newResolveHook = "(JSResolveOp)" + NEWRESOLVE_HOOK_NAME
             classFlags += " | JSCLASS_NEW_RESOLVE"
             enumerateHook = ENUMERATE_HOOK_NAME
-        elif self.descriptor.interface.getExtendedAttribute("Global"):
+        elif self.descriptor.isGlobal():
             newResolveHook = "(JSResolveOp) mozilla::dom::ResolveGlobal"
             classFlags += " | JSCLASS_NEW_RESOLVE"
             enumerateHook = "mozilla::dom::EnumerateGlobal"
@@ -1521,7 +1519,7 @@ def finalizeHook(descriptor, hookName, freeOp):
         finalize += "ClearWrapper(self, self);\n"
     if descriptor.interface.getExtendedAttribute('OverrideBuiltins'):
         finalize += "self->mExpandoAndGeneration.expando = JS::UndefinedValue();\n"
-    if descriptor.interface.getExtendedAttribute("Global"):
+    if descriptor.isGlobal():
         finalize += "mozilla::dom::FinalizeGlobal(CastToJSFreeOp(%s), obj);\n" % freeOp
     finalize += ("AddForDeferredFinalization<%s, %s >(self);\n" %
                  (descriptor.nativeType, DeferredFinalizeSmartPtr(descriptor)))
@@ -2599,7 +2597,7 @@ class CGCreateInterfaceObjectsMethod(CGAbstractMethod):
             interfaceClass = "nullptr"
             interfaceCache = "nullptr"
 
-        isGlobal = self.descriptor.interface.getExtendedAttribute("Global") is not None
+        isGlobal = self.descriptor.isGlobal() is not None
         if not isGlobal and self.properties.hasNonChromeOnly():
             properties = "&sNativeProperties"
         elif self.properties.hasNonChromeOnly():
@@ -7323,7 +7321,7 @@ class CGNewResolveHook(CGAbstractBindingMethod):
             """))
 
     def definition_body(self):
-        if self.descriptor.interface.getExtendedAttribute("Global"):
+        if self.descriptor.isGlobal():
             # Resolve standard classes
             prefix = dedent("""
                 if (!ResolveGlobal(cx, obj, id, objp)) {
@@ -7372,7 +7370,7 @@ class CGEnumerateHook(CGAbstractBindingMethod):
             """))
 
     def definition_body(self):
-        if self.descriptor.interface.getExtendedAttribute("Global"):
+        if self.descriptor.isGlobal():
             # Enumerate standard classes
             prefix = dedent("""
                 if (!EnumerateGlobal(cx, obj)) {
@@ -10666,7 +10664,7 @@ class CGDescriptor(CGThing):
                 if descriptor.interface.hasMembersInSlots():
                     cgThings.append(CGUpdateMemberSlotsMethod(descriptor))
 
-            if descriptor.interface.getExtendedAttribute("Global"):
+            if descriptor.isGlobal():
                 assert descriptor.wrapperCache
                 cgThings.append(CGWrapGlobalMethod(descriptor, properties))
             elif descriptor.wrapperCache:
diff --git a/dom/bindings/Configuration.py b/dom/bindings/Configuration.py
index 6fca0b42d28c..20364185b578 100644
--- a/dom/bindings/Configuration.py
+++ b/dom/bindings/Configuration.py
@@ -563,6 +563,14 @@ class Descriptor(DescriptorProvider):
         """
         return self.hasXPConnectImpls or self.interface.isOnGlobalProtoChain()
 
+    def isGlobal(self):
+        """
+        Returns true if this is the primary interface for a global object
+        of some sort.
+        """
+        return (self.interface.getExtendedAttribute("Global") or
+                self.interface.getExtendedAttribute("PrimaryGlobal"))
+
 # Some utility methods
 def getTypesFromDescriptor(descriptor):
     """
diff --git a/dom/bindings/parser/WebIDL.py b/dom/bindings/parser/WebIDL.py
index 3ff018ea080b..c48f8df06bd5 100644
--- a/dom/bindings/parser/WebIDL.py
+++ b/dom/bindings/parser/WebIDL.py
@@ -224,6 +224,8 @@ class IDLScope(IDLObject):
         # A mapping from global name to the set of global interfaces
         # that have that global name.
         self.globalNameMapping = defaultdict(set)
+        self.primaryGlobalAttr = None
+        self.primaryGlobalName = None
 
     def __str__(self):
         return self.QName()
@@ -643,8 +645,10 @@ class IDLInterface(IDLObjectWithScope):
 
             self.totalMembersInSlots = self.parent.totalMembersInSlots
 
-            # Interfaces with [Global] must not have anything inherit from them
-            if self.parent.getExtendedAttribute("Global"):
+            # Interfaces with [Global] or [PrimaryGlobal] must not
+            # have anything inherit from them
+            if (self.parent.getExtendedAttribute("Global") or
+                self.parent.getExtendedAttribute("PrimaryGlobal")):
                 # Note: This is not a self.parent.isOnGlobalProtoChain() check
                 # because ancestors of a [Global] interface can have other
                 # descendants.
@@ -1106,6 +1110,20 @@ class IDLInterface(IDLObjectWithScope):
                 for globalName in self.globalNames:
                     self.parentScope.globalNameMapping[globalName].add(self.identifier.name)
                 self._isOnGlobalProtoChain = True
+            elif identifier == "PrimaryGlobal":
+                if not attr.noArguments():
+                    raise WebIDLError("[PrimaryGlobal] must take no arguments",
+                                      [attr.location])
+                if self.parentScope.primaryGlobalAttr is not None:
+                    raise WebIDLError(
+                        "[PrimaryGlobal] specified twice",
+                        [attr.location,
+                         self.parentScope.primaryGlobalAttr.location])
+                self.parentScope.primaryGlobalAttr = attr
+                self.parentScope.primaryGlobalName = self.identifier.name
+                self.parentScope.globalNames.add(self.identifier.name)
+                self.parentScope.globalNameMapping[self.identifier.name].add(self.identifier.name)
+                self._isOnGlobalProtoChain = True
             elif (identifier == "NeedNewResolve" or
                   identifier == "OverrideBuiltins" or
                   identifier == "ChromeOnly" or
diff --git a/dom/webidl/Window.webidl b/dom/webidl/Window.webidl
index 33b4f3332cc9..660e3aaeaa48 100644
--- a/dom/webidl/Window.webidl
+++ b/dom/webidl/Window.webidl
@@ -24,7 +24,7 @@ interface nsIDOMCrypto;
 typedef any Transferable;
 
 // http://www.whatwg.org/specs/web-apps/current-work/
-[Global, NeedNewResolve]
+[PrimaryGlobal, NeedNewResolve]
 /*sealed*/ interface Window : EventTarget {
   // the current browsing context
   [Unforgeable, Throws,