diff --git a/xpcom/base/ErrorNames.cpp b/xpcom/base/ErrorNames.cpp
new file mode 100644
index 000000000000..b9bc553d9bf4
--- /dev/null
+++ b/xpcom/base/ErrorNames.cpp
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/ErrorNames.h"
+#include "nsString.h"
+#include "prerror.h"
+
+namespace {
+
+struct ErrorEntry
+{
+  nsresult value;
+  const char * name;
+};
+
+#undef ERROR
+#define ERROR(key, val) {key, #key}
+
+const ErrorEntry errors[] = {
+  #include "ErrorList.h"
+};
+
+#undef ERROR
+
+} // unnamed namespace
+
+namespace mozilla {
+
+void
+GetErrorName(nsresult rv, nsACString& name)
+{
+  for (size_t i = 0; i < ArrayLength(errors); ++i) {
+    if (errors[i].value == rv) {
+      name.AssignASCII(errors[i].name);
+      return;
+    }
+  }
+
+  bool isSecurityError = NS_ERROR_GET_MODULE(rv) == NS_ERROR_MODULE_SECURITY;
+
+  // NS_ERROR_MODULE_SECURITY is the only module that is "allowed" to
+  // synthesize nsresult error codes that are not listed in ErrorList.h. (The
+  // NS_ERROR_MODULE_SECURITY error codes are synthesized from NSPR error
+  // codes.)
+  MOZ_ASSERT(isSecurityError);
+
+  name.AssignASCII(NS_SUCCEEDED(rv) ? "NS_ERROR_GENERATE_SUCCESS("
+                                    : "NS_ERROR_GENERATE_FAILURE(");
+
+  if (isSecurityError) {
+    name.AppendASCII("NS_ERROR_MODULE_SECURITY");
+  } else {
+    // This should never happen given the assertion above, so we don't bother
+    // trying to print a symbolic name for the module here.
+    name.AppendInt(NS_ERROR_GET_MODULE(rv));
+  }
+
+  name.AppendASCII(", ");
+
+  const char * nsprName = nullptr;
+  if (isSecurityError) {
+    // Invert the logic from NSSErrorsService::GetXPCOMFromNSSError
+    PRErrorCode nsprCode
+      = -1 * static_cast<PRErrorCode>(NS_ERROR_GET_CODE(rv));
+    nsprName = PR_ErrorToName(nsprCode);
+
+    // All NSPR error codes defined by NSPR or NSS should have a name mapping.
+    MOZ_ASSERT(nsprName);
+  }
+
+  if (nsprName) {
+    name.AppendASCII(nsprName);
+  } else {
+    name.AppendInt(NS_ERROR_GET_CODE(rv));
+  }
+
+  name.AppendASCII(")");
+}
+
+} // namespace mozilla
diff --git a/xpcom/base/ErrorNames.h b/xpcom/base/ErrorNames.h
new file mode 100644
index 000000000000..1862c0f6791a
--- /dev/null
+++ b/xpcom/base/ErrorNames.h
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_ErrorNames_h
+#define mozilla_ErrorNames_h
+
+#include "nsError.h"
+
+class nsACString;
+
+namespace mozilla {
+
+// Maps the given nsresult to its symbolic name. For example,
+// GetErrorName(NS_OK, name) will result in name == "NS_OK".
+// When the symbolic name is unknown, name will be of the form
+// "NS_ERROR_GENERATE_SUCCESS(<module>, <code>)" or
+// "NS_ERROR_GENERATE_FAILURE(<module>, <code>)".
+void GetErrorName(nsresult rv, nsACString& name);
+
+}
+
+#endif // mozilla_ErrorNames_h
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
index 8c49542465d2..e600314098a0 100644
--- a/xpcom/base/moz.build
+++ b/xpcom/base/moz.build
@@ -76,6 +76,7 @@ EXPORTS.mozilla += [
     'CountingAllocatorBase.h',
     'CycleCollectedJSRuntime.h',
     'Debug.h',
+    'ErrorNames.h',
     'LinuxUtils.h',
     'nsMemoryInfoDumper.h',
     'StackWalk.h',
@@ -97,6 +98,7 @@ UNIFIED_SOURCES += [
     'ClearOnShutdown.cpp',
     'CycleCollectedJSRuntime.cpp',
     'Debug.cpp',
+    'ErrorNames.cpp',
     'nsConsoleMessage.cpp',
     'nsConsoleService.cpp',
     'nsCycleCollector.cpp',