diff --git a/accessible/tests/browser/mac/head.js b/accessible/tests/browser/mac/head.js
index 55203e4d84c2..a99ac2f401be 100644
--- a/accessible/tests/browser/mac/head.js
+++ b/accessible/tests/browser/mac/head.js
@@ -4,7 +4,7 @@
 
 "use strict";
 
-/* exported getNativeInterface, waitForMacEventWithInfo, waitForMacEvent, NSRange */
+/* exported getNativeInterface, waitForMacEventWithInfo, waitForMacEvent, NSRange, NSDictionary */
 
 // Load the shared-head file first.
 /* import-globals-from ../shared-head.js */
@@ -56,3 +56,10 @@ function NSRange(location, length) {
     value: [location, length],
   };
 }
+
+function NSDictionary(dict) {
+  return {
+    objectType: "NSDictionary",
+    object: dict,
+  };
+}
diff --git a/accessible/xpcom/xpcAccessibleMacInterface.h b/accessible/xpcom/xpcAccessibleMacInterface.h
index 950c3dbabd6c..cb969022e03e 100644
--- a/accessible/xpcom/xpcAccessibleMacInterface.h
+++ b/accessible/xpcom/xpcAccessibleMacInterface.h
@@ -71,6 +71,12 @@ class xpcAccessibleMacInterface : public xpcAccessibleMacNSObjectWrapper,
   id JsValueToNSValue(JS::HandleObject aObject, JSContext* aCx,
                       nsresult* aResult);
 
+  // Convert a js value to a specified NSObject. This is called
+  // by JsValueToNSObject when encountering a JS object with
+  // a "object" and "objcetType" property.
+  id JsValueToSpecifiedNSObject(JS::HandleObject aObject, JSContext* aCx,
+                                nsresult* aResult);
+
  private:
   xpcAccessibleMacInterface(const xpcAccessibleMacInterface&) = delete;
   xpcAccessibleMacInterface& operator=(const xpcAccessibleMacInterface&) =
diff --git a/accessible/xpcom/xpcAccessibleMacInterface.mm b/accessible/xpcom/xpcAccessibleMacInterface.mm
index 6b251bbd178a..b7c6d80fc694 100644
--- a/accessible/xpcom/xpcAccessibleMacInterface.mm
+++ b/accessible/xpcom/xpcAccessibleMacInterface.mm
@@ -298,6 +298,16 @@ id xpcAccessibleMacInterface::JsValueToNSObject(JS::HandleValue aValue, JSContex
       return JsValueToNSValue(obj, aCx, aResult);
     }
 
+    bool hasObjectType;
+    bool hasObject;
+    JS_HasOwnProperty(aCx, obj, "objectType", &hasObjectType);
+    JS_HasOwnProperty(aCx, obj, "object", &hasObject);
+    if (hasObjectType && hasObject) {
+      // A js object representing an NSDictionary looks like this:
+      // { objectType: "NSDictionary", value: {k: v, k: v, ...} }
+      return JsValueToSpecifiedNSObject(obj, aCx, aResult);
+    }
+
     // This may be another nsIAccessibleMacInterface instance.
     // If so, return the wrapped NSObject.
     nsCOMPtr<nsIXPConnect> xpc = nsIXPConnect::XPConnect();
@@ -367,6 +377,68 @@ id xpcAccessibleMacInterface::JsValueToNSValue(JS::HandleObject aObject, JSConte
   return nil;
 }
 
+id xpcAccessibleMacInterface::JsValueToSpecifiedNSObject(JS::HandleObject aObject, JSContext* aCx,
+                                                         nsresult* aResult) {
+  *aResult = NS_ERROR_FAILURE;
+  JS::RootedValue objectTypeValue(aCx);
+  if (!JS_GetProperty(aCx, aObject, "objetType", &objectTypeValue)) {
+    NS_WARNING("Could not get objectType");
+    return nil;
+  }
+
+  JS::RootedValue objectValue(aCx);
+  if (!JS_GetProperty(aCx, aObject, "object", &objectValue)) {
+    NS_WARNING("Could not get object");
+    return nil;
+  }
+
+  nsAutoJSString objectType;
+  if (!objectTypeValue.isString() || !objectType.init(aCx, objectTypeValue)) {
+    NS_WARNING("objectType is not a string");
+    return nil;
+  }
+
+  bool isObject = objectValue.isObjectOrNull();
+  if (!isObject) {
+    NS_WARNING("object is not a JSON object");
+    return nil;
+  }
+
+  JS::Rooted<JSObject*> object(aCx, objectValue.toObjectOrNull());
+
+  if (objectType.EqualsLiteral("NSDictionary")) {
+    JS::Rooted<JS::IdVector> ids(aCx, JS::IdVector(aCx));
+    if (!JS_Enumerate(aCx, object, &ids)) {
+      NS_WARNING("Unable to get keys from dictionary object");
+      return nil;
+    }
+
+    NSMutableDictionary* dict = [[NSMutableDictionary alloc] init];
+
+    for (size_t i = 0, n = ids.length(); i < n; i++) {
+      nsresult rv = NS_OK;
+      // get current key
+      JS::RootedValue currentKey(aCx);
+      JS_IdToValue(aCx, ids[i], &currentKey);
+      id unwrappedKey = JsValueToNSObject(currentKey, aCx, &rv);
+      NS_ENSURE_SUCCESS(rv, nil);
+      MOZ_ASSERT([unwrappedKey isKindOfClass:[NSString class]]);
+
+      // get associated value for current key
+      JS::RootedValue currentValue(aCx);
+      JS_GetPropertyById(aCx, object, ids[i], &currentValue);
+      id unwrappedValue = JsValueToNSObject(currentValue, aCx, &rv);
+      NS_ENSURE_SUCCESS(rv, nil);
+      dict[unwrappedKey] = unwrappedValue;
+    }
+
+    *aResult = NS_OK;
+    return dict;
+  }
+
+  return nil;
+}
+
 NS_IMPL_ISUPPORTS(xpcAccessibleMacEvent, nsIAccessibleMacEvent)
 
 xpcAccessibleMacEvent::xpcAccessibleMacEvent(id aNativeObj, id aData)