--- a/dom/base/test/unit/test_range.js
+++ b/dom/base/test/unit/test_range.js
@@ -168,17 +168,20 @@ function getRange(aSourceNode, aFragment
 }
 
 /**
  * Get the document for a given path, and clean it up for our tests.
  *
  * @param aPath The path to the local document.
  */
 function getParsedDocument(aPath) {
-  var doc = do_parse_document(aPath, "application/xml");
+  return do_parse_document(aPath, "application/xml").then(processParsedDocument);
+}
+
+function processParsedDocument(doc) {
   do_check_true(doc.documentElement.localName != "parsererror");
   do_check_true(doc instanceof C_i.nsIDOMXPathEvaluator);
   do_check_true(doc instanceof C_i.nsIDOMDocument);
 
   // Clean out whitespace.
   var walker = doc.createTreeWalker(doc,
                                     C_i.nsIDOMNodeFilter.SHOW_TEXT |
                                     C_i.nsIDOMNodeFilter.SHOW_CDATA_SECTION,
@@ -209,17 +212,20 @@ function getParsedDocument(aPath) {
   return doc;
 }
 
 /**
  * Run the extraction tests.
  */
 function run_extract_test() {
   var filePath = "test_delete_range.xml";
-  var doc = getParsedDocument(filePath);
+  getParsedDocument(filePath).then(do_extract_test);
+}
+
+function do_extract_test(doc) {
   var tests = doc.getElementsByTagName("test");
 
   // Run our deletion, extraction tests.
   for (var i = 0; i < tests.length; i++) {
     dump("Configuring for test " + i + "\n");
     var currentTest = tests.item(i);
 
     // Validate the test is properly formatted for what this harness expects.
@@ -328,17 +334,20 @@ function run_extract_test() {
   }
 }
 
 /**
  * Miscellaneous tests not covered above.
  */
 function run_miscellaneous_tests() {
   var filePath = "test_delete_range.xml";
-  var doc = getParsedDocument(filePath);
+  getParsedDocument(filePath).then(do_miscellaneous_tests);
+}
+
+function do_miscellaneous_tests(doc) {
   var tests = doc.getElementsByTagName("test");
 
   // Let's try some invalid inputs to our DOM range and see what happens.
   var currentTest = tests.item(0);
   var baseSource = currentTest.firstChild;
   var baseResult = baseSource.nextSibling;
   var baseExtract = baseResult.nextSibling;
 

--- a/dom/base/test/unit/test_xmlserializer.js
+++ b/dom/base/test/unit/test_xmlserializer.js
@@ -2,69 +2,81 @@
 /* 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/. */
 
 function xmlEncode(aFile, aFlags, aCharset) {
     if(aFlags == undefined) aFlags = 0;
     if(aCharset == undefined) aCharset = "UTF-8";
 
-    var doc = do_parse_document(aFile, "text/xml");
-
-    var encoder = Components.classes["@mozilla.org/layout/documentEncoder;1?type=text/xml"]
-                   .createInstance(nsIDocumentEncoder);
-    encoder.setCharset(aCharset);
-    encoder.init(doc, "text/xml", aFlags);
-    return encoder.encodeToString();
+    return do_parse_document(aFile, "text/xml").then(doc => {
+      var encoder = Components.classes["@mozilla.org/layout/documentEncoder;1?type=text/xml"]
+                     .createInstance(nsIDocumentEncoder);
+      encoder.setCharset(aCharset);
+      encoder.init(doc, "text/xml", aFlags);
+      return encoder.encodeToString();
+    });
 }
 
 function run_test()
 {
     var result, expected;
     const de = Components.interfaces.nsIDocumentEncoder;
 
-    result = xmlEncode("1_original.xml", de.OutputLFLineBreak);
-    expected =loadContentFile("1_result.xml");
-    do_check_eq(expected, result);
+    xmlEncode("1_original.xml", de.OutputLFLineBreak).then(result => {
+      expected = loadContentFile("1_result.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("2_original.xml", de.OutputLFLineBreak);
-    expected = loadContentFile("2_result_1.xml");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputLFLineBreak).then(result => {
+      expected = loadContentFile("2_result_1.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("2_original.xml", de.OutputCRLineBreak);
-    expected = expected.replace(/\n/g, "\r");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputCRLineBreak).then(result => {
+      expected = expected.replace(/\n/g, "\r");
+      do_check_eq(expected, result);
+    });
 
-    result = xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputCRLineBreak);
-    expected = expected.replace(/\r/mg, "\r\n");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputCRLineBreak).then(result => {
+      expected = expected.replace(/\r/mg, "\r\n");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputFormatted);
-    expected = loadContentFile("2_result_2.xml");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputFormatted).then(result => {
+      expected = loadContentFile("2_result_2.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputFormatted | de.OutputWrap);
-    expected = loadContentFile("2_result_3.xml");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputFormatted | de.OutputWrap).then(result => {
+      expected = loadContentFile("2_result_3.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputWrap);
-    expected = loadContentFile("2_result_4.xml");
-    do_check_eq(expected, result);
+    xmlEncode("2_original.xml", de.OutputLFLineBreak | de.OutputWrap).then(result => {
+      expected = loadContentFile("2_result_4.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("3_original.xml", de.OutputLFLineBreak | de.OutputFormatted | de.OutputWrap);
-    expected = loadContentFile("3_result.xml");
-    do_check_eq(expected, result);
+    xmlEncode("3_original.xml", de.OutputLFLineBreak | de.OutputFormatted | de.OutputWrap).then(result => {
+      expected = loadContentFile("3_result.xml");
+      do_check_eq(expected, result);
+    });
 
-    result =  xmlEncode("3_original.xml", de.OutputLFLineBreak | de.OutputWrap);
-    expected = loadContentFile("3_result_2.xml");
-    do_check_eq(expected, result);
+    xmlEncode("3_original.xml", de.OutputLFLineBreak | de.OutputWrap).then(result => {
+      expected = loadContentFile("3_result_2.xml");
+      do_check_eq(expected, result);
+    });
 
     // tests on namespaces
-    var doc = do_parse_document("4_original.xml", "text/xml");
+    do_parse_document("4_original.xml", "text/xml").then(run_namespace_tests);
+}
 
+function run_namespace_tests(doc) {
+    const de = Components.interfaces.nsIDocumentEncoder;
     var encoder = Components.classes["@mozilla.org/layout/documentEncoder;1?type=text/xml"]
                    .createInstance(nsIDocumentEncoder);
     encoder.setCharset("UTF-8");
     encoder.init(doc, "text/xml", de.OutputLFLineBreak);
 
     result = encoder.encodeToString();
     expected = loadContentFile("4_result_1.xml");
     do_check_eq(expected, result);
@@ -92,10 +104,9 @@ function run_test()
     expected = loadContentFile("4_result_5.xml");
     do_check_eq(expected, result);
 
     encoder.init(doc, "text/xml",  de.OutputLFLineBreak | de.OutputWrap);
     encoder.setWrapColumn(40);
     result = encoder.encodeToString();
     expected = loadContentFile("4_result_6.xml");
     do_check_eq(expected, result);
-
 }

--- a/mobile/android/tests/browser/robocop/robocop_head.js
+++ b/mobile/android/tests/browser/robocop/robocop_head.js
@@ -620,53 +620,16 @@ function do_get_cwd() {
 function do_load_manifest(path) {
   var lf = do_get_file(path);
   const nsIComponentRegistrar = Components.interfaces.nsIComponentRegistrar;
   do_check_true(Components.manager instanceof nsIComponentRegistrar);
   Components.manager.autoRegister(lf);
 }
 
 /**
- * Parse a DOM document.
- *
- * @param aPath File path to the document.
- * @param aType Content type to use in DOMParser.
- *
- * @return nsIDOMDocument from the file.
- */
-function do_parse_document(aPath, aType) {
-  switch (aType) {
-    case "application/xhtml+xml":
-    case "application/xml":
-    case "text/xml":
-      break;
-
-    default:
-      do_throw("type: expected application/xhtml+xml, application/xml or text/xml," +
-                 " got '" + aType + "'",
-               Components.stack.caller);
-  }
-
-  var lf = do_get_file(aPath);
-  const C_i = Components.interfaces;
-  const parserClass = "@mozilla.org/xmlextras/domparser;1";
-  const streamClass = "@mozilla.org/network/file-input-stream;1";
-  var stream = Components.classes[streamClass]
-                         .createInstance(C_i.nsIFileInputStream);
-  stream.init(lf, -1, -1, C_i.nsIFileInputStream.CLOSE_ON_EOF);
-  var parser = Components.classes[parserClass]
-                         .createInstance(C_i.nsIDOMParser);
-  var doc = parser.parseFromStream(stream, null, lf.fileSize, aType);
-  parser = null;
-  stream = null;
-  lf = null;
-  return doc;
-}
-
-/**
  * Registers a function that will run when the test harness is done running all
  * tests.
  *
  * @param aFunction
  *        The function to be called when the test harness has finished running.
  */
 function do_register_cleanup(func) {
   _dump("TEST-INFO | " + _TEST_FILE + " | " +

--- a/testing/xpcshell/head.js
+++ b/testing/xpcshell/head.js
@@ -18,16 +18,17 @@ var _pendingTimers = [];
 var _profileInitialized = false;
 
 // Register the testing-common resource protocol early, to have access to its
 // modules.
 _register_modules_protocol_handler();
 
 var _Promise = Components.utils.import("resource://gre/modules/Promise.jsm", {}).Promise;
 var _PromiseTestUtils = Components.utils.import("resource://testing-common/PromiseTestUtils.jsm", {}).PromiseTestUtils;
+Components.utils.importGlobalProperties(["XMLHttpRequest"]);
 
 // Support a common assertion library, Assert.jsm.
 var AssertCls = Components.utils.import("resource://testing-common/Assert.jsm", null).Assert;
 // Pass a custom report function for xpcshell-test style reporting.
 var Assert = new AssertCls(function(err, message, stack) {
   if (err) {
     do_report_result(false, err.message, err.stack);
   } else {
@@ -1093,30 +1094,31 @@ function do_parse_document(aPath, aType)
       break;
 
     default:
       do_throw("type: expected application/xhtml+xml, application/xml or text/xml," +
                  " got '" + aType + "'",
                Components.stack.caller);
   }
 
-  var lf = do_get_file(aPath);
-  const C_i = Components.interfaces;
-  const parserClass = "@mozilla.org/xmlextras/domparser;1";
-  const streamClass = "@mozilla.org/network/file-input-stream;1";
-  var stream = Components.classes[streamClass]
-                         .createInstance(C_i.nsIFileInputStream);
-  stream.init(lf, -1, -1, C_i.nsIFileInputStream.CLOSE_ON_EOF);
-  var parser = Components.classes[parserClass]
-                         .createInstance(C_i.nsIDOMParser);
-  var doc = parser.parseFromStream(stream, null, lf.fileSize, aType);
-  parser = null;
-  stream = null;
-  lf = null;
-  return doc;
+  let file = do_get_file(aPath),
+      ios = Components.classes['@mozilla.org/network/io-service;1']
+            .getService(Components.interfaces.nsIIOService),
+      url = ios.newFileURI(file).spec;
+  file = null;
+  return new Promise((resolve, reject) => {
+    let xhr = new XMLHttpRequest();
+    xhr.open("GET", url);
+    xhr.responseType = "document";
+    xhr.onerror = reject;
+    xhr.onload = () => {
+      resolve(xhr.response);
+    };
+    xhr.send();
+  });
 }
 
 /**
  * Registers a function that will run when the test harness is done running all
  * tests.
  *
  * @param aFunction
  *        The function to be called when the test harness has finished running.