--- a/dom/webidl/Navigator.webidl
+++ b/dom/webidl/Navigator.webidl
@@ -185,27 +185,27 @@ interface NavigatorMobileId {
     [NewObject, Func="Navigator::HasMobileIdSupport"]
     Promise<any> getMobileIdAssertion(optional MobileIdOptions options);
 };
 Navigator implements NavigatorMobileId;
 #endif // MOZ_B2G
 
 // nsIDOMNavigator
 partial interface Navigator {
-  [Throws]
+  [Throws, Constant, Cached]
   readonly attribute DOMString oscpu;
   // WebKit/Blink support this; Trident/Presto do not.
   readonly attribute DOMString vendor;
   // WebKit/Blink supports this (hardcoded ""); Trident/Presto do not.
   readonly attribute DOMString vendorSub;
   // WebKit/Blink supports this (hardcoded "20030107"); Trident/Presto don't
   readonly attribute DOMString productSub;
   // WebKit/Blink/Trident/Presto support this.
   readonly attribute boolean cookieEnabled;
-  [Throws]
+  [Throws, Constant, Cached]
   readonly attribute DOMString buildID;
   [Throws, CheckAnyPermissions="power", UnsafeInPrerendering]
   readonly attribute MozPowerManager mozPower;
 
   // WebKit/Blink/Trident/Presto support this.
   [Throws]
   boolean javaEnabled();