diff --git a/dom/xhr/XMLHttpRequestMainThread.cpp b/dom/xhr/XMLHttpRequestMainThread.cpp
index 078223d671f0..4fc0a7c19867 100644
--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -3104,7 +3104,6 @@ XMLHttpRequestMainThread::OverrideMimeType(const nsAString& aMimeType,
 
   if (mState == XMLHttpRequest_Binding::LOADING ||
       mState == XMLHttpRequest_Binding::DONE) {
-    ResetResponse();
     aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE);
     return;
   }
diff --git a/dom/xhr/tests/test_xhr_overridemimetype_throws_on_invalid_state.html b/dom/xhr/tests/test_xhr_overridemimetype_throws_on_invalid_state.html
index bdbbf1591539..0491fe2fca1c 100644
--- a/dom/xhr/tests/test_xhr_overridemimetype_throws_on_invalid_state.html
+++ b/dom/xhr/tests/test_xhr_overridemimetype_throws_on_invalid_state.html
@@ -17,10 +17,10 @@ function onWindowLoad() {
 
 function runTest() {
   var testFunctions = [
-    function() { testOverMimeTypeThrowsDuringReadyState(3, "application/xml"); },
-    function() { testOverMimeTypeThrowsDuringReadyState(3, "application/xml;charset=Shift-JIS"); },
-    function() { testOverMimeTypeThrowsDuringReadyState(4, "application/xml"); },
-    function() { testOverMimeTypeThrowsDuringReadyState(4, "application/xml;charset=Shift-JIS"); },
+    function() { testOverMimeTypeThrowsDuringReadyState(3, "text/plain"); },
+    function() { testOverMimeTypeThrowsDuringReadyState(3, "text/plain;charset=Shift-JIS"); },
+    function() { testOverMimeTypeThrowsDuringReadyState(4, "text/plain"); },
+    function() { testOverMimeTypeThrowsDuringReadyState(4, "text/plain;charset=Shift-JIS"); },
   ];
 
   function nextTest() {
@@ -47,8 +47,9 @@ function runTest() {
         }
       }
       if (xhr.readyState === 4) {
-        is(xhr.responseXML, null, "responseXML was not null" +
-                                  " for readyState=" + readyState + ", mimeType=" + mimeType);
+        isnot(xhr.responseXML, null, "responseXML was null" +
+                                     " for readyState=" + readyState +
+                                     ", mimeType=" + mimeType);
         nextTest();
       }
     }
diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 8f392ff46009..ea5951e22f18 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -633267,7 +633267,7 @@
    "testharness"
   ],
   "xhr/overridemimetype-done-state.any.js": [
-   "bbdf30a044795788f81e6e7addbdc3355fe93fa4",
+   "5924cec26f0bf551a7d37969a62941fc88c177f1",
    "testharness"
   ],
   "xhr/overridemimetype-edge-cases.window.js": [
@@ -633755,7 +633755,7 @@
    "testharness"
   ],
   "xhr/responsetype.any.js": [
-   "8c5d86795c3a88e485990a31e95619b77ab0360c",
+   "eda46254f0b786635b91fdd7f2b63992f2f9ad5d",
    "testharness"
   ],
   "xhr/responseurl.html": [
diff --git a/testing/web-platform/tests/xhr/overridemimetype-done-state.any.js b/testing/web-platform/tests/xhr/overridemimetype-done-state.any.js
index ca9fbaa7e9ac..bdf49e1ca52e 100644
--- a/testing/web-platform/tests/xhr/overridemimetype-done-state.any.js
+++ b/testing/web-platform/tests/xhr/overridemimetype-done-state.any.js
@@ -7,10 +7,13 @@ var test = async_test();
 var client = new XMLHttpRequest();
 client.onreadystatechange = test.step_func( function() {
   if (client.readyState !== 4) return;
+  var text = client.responseText;
+  assert_not_equals(text, "");
   assert_throws("InvalidStateError", function() { client.overrideMimeType('application/xml;charset=Shift-JIS'); });
   if (GLOBAL.isWindow()) {
     assert_equals(client.responseXML, null);
   }
+  assert_equals(client.responseText, text);
   test.done();
 });
 client.open("GET", "resources/status.py?type="+encodeURIComponent('text/plain;charset=iso-8859-1')+'&content=%3Cmsg%3E%83%65%83%58%83%67%3C%2Fmsg%3E');
diff --git a/testing/web-platform/tests/xhr/responsetype.any.js b/testing/web-platform/tests/xhr/responsetype.any.js
index 17788e4782ce..88bd9189ebed 100644
--- a/testing/web-platform/tests/xhr/responsetype.any.js
+++ b/testing/web-platform/tests/xhr/responsetype.any.js
@@ -85,6 +85,8 @@ types.forEach(function(type) {
     xhr.open('get', '/');
     xhr.onreadystatechange = this.step_func(function() {
       if (xhr.readyState === XMLHttpRequest.DONE) {
+        var text = xhr.responseText;
+        assert_not_equals(text, "");
         if (isIgnoredType(type)) {
           xhr.responseType = type;
         } else {
@@ -93,6 +95,7 @@ types.forEach(function(type) {
           });
         }
         assert_equals(xhr.responseType, "");
+        assert_equals(xhr.responseText, text);
         this.done();
       }
     });