--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -980,17 +980,16 @@ void Navigator::CheckProtocolHandlerAllo
   if (!Preferences::GetBool(specificPref.get(), defaultExternal)) {
     raisePermissionDeniedScheme();
     return;
   }
 }
 
 void Navigator::RegisterProtocolHandler(const nsAString& aScheme,
                                         const nsAString& aURI,
-                                        const nsAString& aTitle,
                                         ErrorResult& aRv) {
   if (!mWindow || !mWindow->GetOuterWindow() || !mWindow->GetDocShell() ||
       !mWindow->GetDoc()) {
     return;
   }
   nsCOMPtr<nsILoadContext> loadContext = do_GetInterface(mWindow);
   if (loadContext->UsePrivateBrowsing()) {
     // If we're a private window, don't alert the user or webpage. We log to the
@@ -1009,30 +1008,34 @@ void Navigator::RegisterProtocolHandler(
   nsCOMPtr<nsIURI> handlerURI;
   NS_NewURI(getter_AddRefs(handlerURI), NS_ConvertUTF16toUTF8(aURI),
             doc->GetDocumentCharacterSet(), docURI);
   CheckProtocolHandlerAllowed(aScheme, handlerURI, docURI, aRv);
   if (aRv.Failed()) {
     return;
   }
 
+  // Determine a title from the document URI.
+  nsAutoCString docDisplayHostPort;
+  docURI->GetDisplayHostPort(docDisplayHostPort);
+  NS_ConvertASCIItoUTF16 title(docDisplayHostPort);
+
   if (XRE_IsContentProcess()) {
     nsAutoString scheme(aScheme);
-    nsAutoString title(aTitle);
     RefPtr<BrowserChild> browserChild = BrowserChild::GetFrom(mWindow);
     browserChild->SendRegisterProtocolHandler(scheme, handlerURI, title,
                                               docURI);
     return;
   }
 
   nsCOMPtr<nsIWebProtocolHandlerRegistrar> registrar =
       do_GetService(NS_WEBPROTOCOLHANDLERREGISTRAR_CONTRACTID);
   if (registrar) {
-    aRv = registrar->RegisterProtocolHandler(aScheme, handlerURI, aTitle,
-                                             docURI, mWindow->GetOuterWindow());
+    aRv = registrar->RegisterProtocolHandler(aScheme, handlerURI, title, docURI,
+                                             mWindow->GetOuterWindow());
   }
 }
 
 Geolocation* Navigator::GetGeolocation(ErrorResult& aRv) {
   if (mGeolocation) {
     return mGeolocation;
   }
 

--- a/dom/base/Navigator.h
+++ b/dom/base/Navigator.h
@@ -118,17 +118,17 @@ class Navigator final : public nsISuppor
                    ErrorResult& aRv) const;
   void GetUserAgent(nsAString& aUserAgent, CallerType aCallerType,
                     ErrorResult& aRv) const;
   bool OnLine();
   void CheckProtocolHandlerAllowed(const nsAString& aScheme,
                                    nsIURI* aHandlerURI, nsIURI* aDocumentURI,
                                    ErrorResult& aRv);
   void RegisterProtocolHandler(const nsAString& aScheme, const nsAString& aURL,
-                               const nsAString& aTitle, ErrorResult& aRv);
+                               ErrorResult& aRv);
   nsMimeTypeArray* GetMimeTypes(ErrorResult& aRv);
   nsPluginArray* GetPlugins(ErrorResult& aRv);
   Permissions* GetPermissions(ErrorResult& aRv);
   void GetDoNotTrack(nsAString& aResult);
   Geolocation* GetGeolocation(ErrorResult& aRv);
   Promise* GetBattery(ErrorResult& aRv);
 
   Promise* Share(const ShareData& aData, ErrorResult& aRv);

--- a/dom/webidl/Navigator.webidl
+++ b/dom/webidl/Navigator.webidl
@@ -79,17 +79,17 @@ interface mixin NavigatorOnLine {
   readonly attribute boolean onLine;
 };
 
 interface mixin NavigatorContentUtils {
   // content handler registration
   [Throws, ChromeOnly]
   void checkProtocolHandlerAllowed(DOMString scheme, URI handlerURI, URI documentURI);
   [Throws, SecureContext]
-  void registerProtocolHandler(DOMString scheme, DOMString url, DOMString title);
+  void registerProtocolHandler(DOMString scheme, DOMString url);
   // NOT IMPLEMENTED
   //void unregisterProtocolHandler(DOMString scheme, DOMString url);
 };
 
 [SecureContext]
 interface mixin NavigatorStorage {
   [Pref="dom.storageManager.enabled"]
   readonly attribute StorageManager storage;

--- a/testing/web-platform/meta/html/dom/idlharness.https.html.ini
+++ b/testing/web-platform/meta/html/dom/idlharness.https.html.ini
@@ -706,19 +706,16 @@ prefs: [dom.security.featurePolicy.exper
     expected: FAIL
 
   [OffscreenCanvas interface: operation convertToBlob(optional ImageEncodeOptions)]
     expected: FAIL
 
   [OffscreenCanvasRenderingContext2D interface: operation arc(unrestricted double, unrestricted double, unrestricted double, unrestricted double, unrestricted double, optional boolean)]
     expected: FAIL
 
-  [Navigator interface: operation registerProtocolHandler(DOMString, USVString)]
-    expected: FAIL
-
   [ElementInternals interface: operation setValidity(optional ValidityStateFlags, optional DOMString, optional HTMLElement)]
     expected: FAIL
 
   [ElementInternals interface: attribute shadowRoot]
     expected: FAIL
 
 
 [idlharness.https.html?include=(Document|Window)]

deleted file mode 100644
--- a/testing/web-platform/meta/html/webappapis/system-state-and-capabilities/the-navigator-object/historical.https.window.js.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[historical.https.window.html]
-  [registerProtocolHandler has no third argument]
-    expected: FAIL
-