diff --git a/dom/permission/Permissions.cpp b/dom/permission/Permissions.cpp
index fc6c06d054eb..a74f65b80cbc 100644
--- a/dom/permission/Permissions.cpp
+++ b/dom/permission/Permissions.cpp
@@ -142,26 +142,20 @@ already_AddRefed<Promise> Permissions::Query(JSContext* aCx,
 }
 
 already_AddRefed<PermissionStatus> Permissions::ParseSetParameters(
-    JSContext* aCx, JS::Handle<JSObject*> aParameters, ErrorResult& aRv) {
+    JSContext* aCx, const PermissionSetParameters& aParameters,
+    ErrorResult& aRv) {
   // Step 1: Let parametersDict be the parameters argument, converted to an IDL
   // value of type PermissionSetParameters. If this throws an exception,
   // return an invalid argument error.
-  // (The error type should be handled by the caller)
-  JS::Rooted<JS::Value> parameters(aCx, JS::ObjectValue(*aParameters));
-  RootedDictionary<PermissionSetParameters> parametersDict(aCx);
-  if (!parametersDict.Init(aCx, parameters)) {
-    aRv.MightThrowJSException();
-    aRv.StealExceptionFromJSContext(aCx);
-    return nullptr;
-  }
+  // (Done by IDL layer, and the error type should be handled by the caller)
 
-  // Step 2: Let rootDesc be parameters.descriptor.
-  JS::Rooted<JSObject*> rootDesc(aCx, parametersDict.mDescriptor);
-
-  // Step 3: If parameters.state is an inappropriate permission state for any
-  // implementation-defined reason, return a invalid argument error.
+  // Step 2: If parametersDict.state is an inappropriate permission state for
+  // any implementation-defined reason, return a invalid argument error.
   // (We don't do this)
 
+  // Step 3: Let rootDesc be parametersDict.descriptor.
+  JS::Rooted<JSObject*> rootDesc(aCx, aParameters.mDescriptor);
+
   // Step 4: Let typedDescriptor be the object rootDesc refers to, converted
   // to an IDL value of rootDesc.name's permission descriptor type. If this
   // throws an exception, return a invalid argument error.
@@ -174,7 +168,7 @@ already_AddRefed<PermissionStatus> Permissions::ParseSetParameters(
   }
 
   // Set the state too so that the caller can use it for step 5.
-  status->SetState(parametersDict.mState);
+  status->SetState(aParameters.mState);
 
   return status.forget();
 }
diff --git a/dom/permission/Permissions.h b/dom/permission/Permissions.h
index 86087ef4aac7..f6cfd4ae6568 100644
--- a/dom/permission/Permissions.h
+++ b/dom/permission/Permissions.h
@@ -19,6 +19,7 @@ namespace dom {
 
 class Promise;
 class PermissionStatus;
+struct PermissionSetParameters;
 
 class Permissions final : public nsISupports, public nsWrapperCache {
  public:
@@ -39,7 +40,8 @@ class Permissions final : public nsISupports, public nsWrapperCache {
   // The IDL conversion steps of
   // https://w3c.github.io/permissions/#webdriver-command-set-permission
   already_AddRefed<PermissionStatus> ParseSetParameters(
-      JSContext* aCx, JS::Handle<JSObject*> aParameters, ErrorResult& aRv);
+      JSContext* aCx, const PermissionSetParameters& aParameters,
+      ErrorResult& aRv);
 
  private:
   ~Permissions();
diff --git a/dom/webidl/Permissions.webidl b/dom/webidl/Permissions.webidl
index 93d5a573d1ce..c4804e79cb0e 100644
--- a/dom/webidl/Permissions.webidl
+++ b/dom/webidl/Permissions.webidl
@@ -37,8 +37,6 @@ interface Permissions {
   Promise<PermissionStatus> query(object permission);
 
   // http://w3c.github.io/permissions/#webdriver-command-set-permission
-  // We use `object` instead of PermissionSetParameters here to retain the access
-  // to the extra descriptor members from e.g. MidiPermissionDescriptor.
   [ChromeOnly, Throws]
-  PermissionStatus parseSetParameters(object parameters);
+  PermissionStatus parseSetParameters(PermissionSetParameters parameters);
 };