Bug 1876392: Ensure selector existence in MOXAccessibleBase moxUnignoredParent. r=eeejay

Differential Revision: https://phabricator.services.mozilla.com/D199585

accessible/mac/MOXAccessibleBase.mm

@@ -495,10 +495,19 @@ mozilla::LogModule* GetMacAccessibilityLog() {
 }
 
 - (id<mozAccessible>)moxUnignoredParent {
-  id nativeParent = [self moxParent];
+  id<mozAccessible> nativeParent = [self moxParent];
+  if (!nativeParent) {
+    return nil;
+  }
 
   if (![nativeParent isAccessibilityElement]) {
-    return [nativeParent moxUnignoredParent];
+    if ([nativeParent conformsToProtocol:@protocol(MOXAccessible)] &&
+        [nativeParent respondsToSelector:@selector(moxUnignoredParent)]) {
+      // Cast away the protocol so we can cast to another protocol.
+      id bareNativeParent = nativeParent;
+      id<MOXAccessible> moxNativeParent = bareNativeParent;
+      return [moxNativeParent moxUnignoredParent];
+    }
   }
 
   return GetObjectOrRepresentedView(nativeParent);