--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -1467,23 +1467,25 @@ XMLHttpRequestMainThread::Open(const nsA
 
   // Step 7
   // This is already handled by the other Open() method, which passes
   // username and password in as NullStrings.
 
   // Step 8
   nsAutoCString host;
   parsedURL->GetHost(host);
-  if (!host.IsEmpty()) {
-    if (!aUsername.IsVoid() || !aPassword.IsVoid()) {
-      Unused << NS_MutateURI(parsedURL)
-                  .SetUsername(NS_ConvertUTF16toUTF8(aUsername))
-                  .SetPassword(NS_ConvertUTF16toUTF8(aPassword))
-                  .Finalize(parsedURL);
+  if (!host.IsEmpty() && (!aUsername.IsVoid() || !aPassword.IsVoid())) {
+    auto mutator = NS_MutateURI(parsedURL);
+    if (!aUsername.IsVoid()) {
+      mutator.SetUsername(NS_ConvertUTF16toUTF8(aUsername));
     }
+    if (!aPassword.IsVoid()) {
+      mutator.SetPassword(NS_ConvertUTF16toUTF8(aPassword));
+    }
+    Unused << mutator.Finalize(parsedURL);
   }
 
   // Step 9
   if (!aAsync && HasOrHasHadOwner() && (mTimeoutMilliseconds ||
        mResponseType != XMLHttpRequestResponseType::_empty)) {
     if (mTimeoutMilliseconds) {
       LogMessage("TimeoutSyncXHRWarning", GetOwner());
     }

--- a/testing/web-platform/meta/xhr/send-authentication-competing-names-passwords.htm.ini
+++ b/testing/web-platform/meta/xhr/send-authentication-competing-names-passwords.htm.ini
@@ -6,17 +6,8 @@
     expected: FAIL
 
   [XMLHttpRequest user/pass options: pass in URL, user in open()]
     expected: FAIL
 
   [XMLHttpRequest user/pass options: pass in URL, user/pass in open()]
     expected: FAIL
 
-  [XMLHttpRequest user/pass options: user in URL, pass in open()]
-    expected: FAIL
-
-  [XMLHttpRequest user/pass options: user/pass in URL; user in open()]
-    expected: FAIL
-
-  [XMLHttpRequest user/pass options: user/pass in URL; pass in open()]
-    expected: FAIL
-