Bug 1738070: Don't fire state change a11y events for NS_EVENT_STATE_DEFAULT changes on things other than buttons. r=morgan

We only expose this state on HTMLButtonAccessible, but we sometimes get these notifications for other controls; e.g. checkbox inputs.
We shouldn't fire a state change event for a state we never expose.

Differential Revision: https://phabricator.services.mozilla.com/D129673

accessible/generic/DocAccessible.cpp

@@ -880,7 +880,9 @@ void DocAccessible::ContentStateChanged(dom::Document* aDocument,
     FireDelayedEvent(event);
   }
 
-  if (aStateMask.HasState(NS_EVENT_STATE_DEFAULT)) {
+  // We only expose NS_EVENT_STATE_DEFAULT on buttons, but we can get
+  // notifications for other controls like checkboxes.
+  if (aStateMask.HasState(NS_EVENT_STATE_DEFAULT) && accessible->IsButton()) {
     RefPtr<AccEvent> event =
         new AccStateChangeEvent(accessible, states::DEFAULT);
     FireDelayedEvent(event);