diff --git a/browser/base/content/test/browser_bug561636.js b/browser/base/content/test/browser_bug561636.js
index a14169b5e1e3..d8b7f8b9608f 100644
--- a/browser/base/content/test/browser_bug561636.js
+++ b/browser/base/content/test/browser_bug561636.js
@@ -355,7 +355,7 @@ function test9()
       gBrowser.removeTab(tab, {animate: false});
 
       // Next test
-      executeSoon(test10);
+      executeSoon(finish);
     });
   };
 
@@ -372,38 +372,3 @@ function test9()
 
   tab.linkedBrowser.loadURI(uri);
 }
-
-/**
- * In this test, we check that the author defined error message is shown.
- */
-function test10()
-{
-  let uri = "data:text/html,<iframe name='t'></iframe><form target='t' action='data:text/html,'><input x-moz-errormessage='foo' required id='i'><input id='s' type='submit'></form>";
-  let tab = gBrowser.addTab();
-
-  gInvalidFormPopup.addEventListener("popupshown", function() {
-    gInvalidFormPopup.removeEventListener("popupshown", arguments.callee, false);
-
-    let doc = gBrowser.contentDocument;
-    is(doc.activeElement, doc.getElementById('i'),
-       "First invalid element should be focused");
-
-    checkPopupShow();
-
-    is(gInvalidFormPopup.firstChild.nodeValue, "foo",
-       "The panel should show the author defined error message");
-
-    // Clean-up and next test.
-    gBrowser.removeTab(gBrowser.selectedTab, {animate: false});
-    executeSoon(finish);
-  }, false);
-
-  tab.linkedBrowser.addEventListener("load", function(aEvent) {
-    tab.linkedBrowser.removeEventListener("load", arguments.callee, true);
-
-    gBrowser.contentDocument.getElementById('s').click();
-  }, true);
-
-  gBrowser.selectedTab = tab;
-  gBrowser.selectedTab.linkedBrowser.loadURI(uri);
-}
diff --git a/content/base/src/nsGkAtomList.h b/content/base/src/nsGkAtomList.h
index 9ba295d94bb0..1d5e650774e8 100644
--- a/content/base/src/nsGkAtomList.h
+++ b/content/base/src/nsGkAtomList.h
@@ -588,7 +588,6 @@ GK_ATOM(mouseover, "mouseover")
 GK_ATOM(mousethrough, "mousethrough")
 GK_ATOM(mouseup, "mouseup")
 GK_ATOM(moz_opaque, "moz-opaque")
-GK_ATOM(x_moz_errormessage, "x-moz-errormessage")
 GK_ATOM(msthemecompatible, "msthemecompatible")
 GK_ATOM(multicol, "multicol")
 GK_ATOM(multiple, "multiple")
diff --git a/content/html/content/src/nsIConstraintValidation.cpp b/content/html/content/src/nsIConstraintValidation.cpp
index ca4d18be3b4f..c24603fc6648 100644
--- a/content/html/content/src/nsIConstraintValidation.cpp
+++ b/content/html/content/src/nsIConstraintValidation.cpp
@@ -78,16 +78,7 @@ nsIConstraintValidation::GetValidationMessage(nsAString& aValidationMessage)
   aValidationMessage.Truncate();
 
   if (IsCandidateForConstraintValidation() && !IsValid()) {
-    nsCOMPtr<nsIContent> content = do_QueryInterface(this);
-    NS_ASSERTION(content, "This class should be inherited by HTML elements only!");
-
-    nsAutoString authorMessage;
-    content->GetAttr(kNameSpaceID_None, nsGkAtoms::x_moz_errormessage,
-                     authorMessage);
-
-    if (!authorMessage.IsEmpty()) {
-      aValidationMessage.Assign(authorMessage);
-    } else if (GetValidityState(VALIDITY_STATE_CUSTOM_ERROR)) {
+    if (GetValidityState(VALIDITY_STATE_CUSTOM_ERROR)) {
       aValidationMessage.Assign(mCustomValidity);
     } else if (GetValidityState(VALIDITY_STATE_TOO_LONG)) {
       GetValidationMessage(aValidationMessage, VALIDITY_STATE_TOO_LONG);
diff --git a/content/html/content/test/Makefile.in b/content/html/content/test/Makefile.in
index a475d4bcb658..defeed6295a1 100644
--- a/content/html/content/test/Makefile.in
+++ b/content/html/content/test/Makefile.in
@@ -230,7 +230,6 @@ _TEST_FILES = \
 		test_bug557087-4.html \
 		test_bug557087-5.html \
 		test_bug557087-6.html \
-		test_bug600155.html \
 		test_bug598643.html \
 		test_bug596350.html \
 		$(NULL)
diff --git a/content/html/content/test/test_bug600155.html b/content/html/content/test/test_bug600155.html
deleted file mode 100644
index 16aead12508a..000000000000
--- a/content/html/content/test/test_bug600155.html
+++ /dev/null
@@ -1,45 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=600155
--->
-<head>
-  <title>Test for Bug 600155</title>
-  <script type="application/javascript" src="/MochiKit/packed.js"></script>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=600155">Mozilla Bug 600155</a>
-<p id="display"></p>
-<div id='content' style='display:none;'>
-</div>
-<pre id="test">
-<script type="application/javascript">
-
-/** Test for Bug 600155 **/
-
-var subjectForConstraintValidation = [ "button", "input", "select", "textarea" ];
-var content = document.getElementById('content');
-
-for each (var eName in subjectForConstraintValidation) {
-  var e = document.createElement(eName);
-  content.appendChild(e);
-  e.setAttribute("x-moz-errormessage", "foo");
-  if ("required" in e) {
-    e.required = true;
-  } else {
-    e.setCustomValidity("bar");
-  }
-
-  // At this point, the element is invalid.
-  is(e.validationMessage, "foo",
-     "the validation message should be the author one");
-
-  content.removeChild(e);
-}
-
-</script>
-</pre>
-</body>
-</html>
