--- a/mobile/android/modules/moz.build
+++ b/mobile/android/modules/moz.build
@@ -14,17 +14,16 @@ EXTRA_JS_MODULES += [
     'HelperApps.jsm',
     'Home.jsm',
     'HomeProvider.jsm',
     'JavaAddonManager.jsm',
     'JNI.jsm',
     'LightweightThemeConsumer.jsm',
     'MediaPlayerApp.jsm',
     'Messaging.jsm',
-    'MulticastDNS.jsm',
     'NetErrorHelper.jsm',
     'Notifications.jsm',
     'OrderedBroadcast.jsm',
     'PageActions.jsm',
     'Prompt.jsm',
     'RuntimePermissions.jsm',
     'Sanitizer.jsm',
     'SharedPreferences.jsm',

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -1883,16 +1883,19 @@ pref("network.proxy.autoconfig_url", "")
 // If we cannot load the PAC file, then try again (doubling from interval_min
 // until we reach interval_max or the PAC file is successfully loaded).
 pref("network.proxy.autoconfig_retry_interval_min", 5);    // 5 seconds
 pref("network.proxy.autoconfig_retry_interval_max", 300);  // 5 minutes
 
 // Use the HSTS preload list by default
 pref("network.stricttransportsecurity.preloadlist", true);
 
+// Use JS mDNS as a fallback
+pref("network.mdns.use_js_fallback", false);
+
 pref("converter.html2txt.structs",          true); // Output structured phrases (strong, em, code, sub, sup, b, i, u)
 pref("converter.html2txt.header_strategy",  1); // 0 = no indention; 1 = indention, increased with header level; 2 = numbering and slight indention
 // Whether we include ruby annotation in the text despite whether it
 // is requested. This was true because we didn't explicitly strip out
 // annotations. Set false by default to provide a better behavior, but
 // we want to be able to pref-off it if user doesn't like it.
 pref("converter.html2txt.always_include_ruby", false);
 

rename from mobile/android/modules/MulticastDNS.jsm
rename to netwerk/dns/mdns/libmdns/MulticastDNSAndroid.jsm

new file mode 100644
--- /dev/null
+++ b/netwerk/dns/mdns/libmdns/MulticastDNSFallback.jsm
@@ -0,0 +1,577 @@
+/* -*- Mode: js; js-indent-level: 2; indent-tabs-mode: nil; tab-width: 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/. */
+/* jshint esnext: true, moz: true */
+
+'use strict';
+
+this.EXPORTED_SYMBOLS = ['MulticastDNS'];
+
+const { classes: Cc, interfaces: Ci, utils: Cu, results: Cr } = Components;
+
+Cu.import('resource://gre/modules/Services.jsm');
+Cu.import('resource://gre/modules/XPCOMUtils.jsm');
+
+const MDNS_PORT = 5353;
+const MDNS_ADDRESS = '224.0.0.251';
+
+const DNS_REC_TYPE_PTR = 12;
+const DNS_REC_TYPE_TXT = 16;
+const DNS_REC_TYPE_SRV = 33;
+const DNS_REC_TYPE_A   = 1;
+const DNS_REC_TYPE_NSEC= 47;
+
+const DNS_CLASS_QU = 0x8000;
+const DNS_CLASS_IN = 0x0001;
+
+const DNS_SECTION_QD = 'qd';
+const DNS_SECTION_AN = 'an';
+const DNS_SECTION_NS = 'ns';
+const DNS_SECTION_AR = 'ar';
+
+const DEBUG = false;
+
+function debug(msg) {
+  Services.console.logStringMessage('MulticastDNSFallback: ' + msg);
+}
+
+/* The following was taken from https://raw.githubusercontent.com/GoogleChrome/chrome-app-samples/master/mdns-browser/dns.js */
+
+/**
+ * DataWriter writes data to an ArrayBuffer, presenting it as the instance
+ * variable 'buffer'.
+ *
+ * @constructor
+ */
+let DataWriter = function(opt_size) {
+  let loc = 0;
+  let view = new Uint8Array(new ArrayBuffer(opt_size || 512));
+
+  this.byte_ = function(v) {
+    view[loc] = v;
+    ++loc;
+    this.buffer = view.buffer.slice(0, loc);
+  }.bind(this);
+};
+
+DataWriter.prototype.byte = function(v) {
+  this.byte_(v);
+  return this;
+};
+
+DataWriter.prototype.short = function(v) {
+  return this.byte((v >> 8) & 0xff).byte(v & 0xff);
+};
+
+DataWriter.prototype.long = function(v) {
+  return this.short((v >> 16) & 0xffff).short(v & 0xffff);
+};
+
+/**
+ * Writes a DNS name. If opt_ref is specified, will finish this name with a
+ * suffix reference (i.e., 0xc0 <ref>). If not, then will terminate with a NULL
+ * byte.
+ */
+DataWriter.prototype.name = function(v, opt_ref) {
+  let parts = v.split('.');
+  parts.forEach(function(part) {
+    this.byte(part.length);
+    for (let i = 0; i < part.length; ++i) {
+      this.byte(part.charCodeAt(i));
+    }
+  }.bind(this));
+  if (opt_ref) {
+    this.byte(0xc0).byte(opt_ref);
+  } else {
+    this.byte(0);
+  }
+  return this;
+};
+
+/**
+ * DataConsumer consumes data from an ArrayBuffer.
+ *
+ * @constructor
+ */
+let DataConsumer = function(arg) {
+  if (arg instanceof Uint8Array) {
+    this.view_ = arg;
+  } else {
+    this.view_ = new Uint8Array(arg);
+  }
+  this.loc_ = 0;
+};
+
+/**
+ * @return whether this DataConsumer has consumed all its data
+ */
+DataConsumer.prototype.isEOF = function() {
+  return this.loc_ >= this.view_.byteLength;
+};
+
+/**
+ * @param length {integer} number of bytes to return from the front of the view
+ * @return a Uint8Array
+ */
+DataConsumer.prototype.slice = function(length) {
+  let view = this.view_.subarray(this.loc_, this.loc_ + length);
+  this.loc_ += length;
+  return view;
+};
+
+DataConsumer.prototype.byte = function() {
+  this.loc_ += 1;
+  return this.view_[this.loc_ - 1];
+};
+
+DataConsumer.prototype.short = function() {
+  return (this.byte() << 8) + this.byte();
+};
+
+DataConsumer.prototype.long = function() {
+  return (this.short() << 16) + this.short();
+};
+
+/**
+ * Consumes a DNS name, which will finish with a NULL byte.
+ */
+DataConsumer.prototype.name = function() {
+  let parts = [];
+  for (;;) {
+    let len = this.byte();
+    if (!len) {
+      break;
+    } else if (len == 0xc0) {
+      // concat suffix reference (i.e., 0xc0 <ref>).
+      let ref = this.byte();
+      let refConsumer = new DataConsumer(new Uint8Array(this.view_.buffer, ref));
+      parts.push(refConsumer.name());
+      break;
+    }
+
+    // Otherwise, consume a string!
+    let v = '';
+    while (len-- > 0) {
+      v += String.fromCharCode(this.byte());
+    }
+    parts.push(v);
+  }
+  return parts.join('.');
+};
+
+/**
+ * Consumes a string according to length.
+ */
+DataConsumer.prototype.string = function() {
+  let len = this.byte();
+  if (!len) {
+    return;
+  }
+
+  let v = '';
+  while (len-- > 0) {
+    v += String.fromCharCode(this.byte());
+  }
+  return v;
+};
+
+/**
+ * DNSPacket holds the state of a DNS packet. It can be modified or serialized
+ * in-place.
+ *
+ * @constructor
+ */
+let DNSPacket = function(opt_flags) {
+  this.flags_ = opt_flags || 0; /* uint16 */
+  this.data_ = {};
+  this.data_[DNS_SECTION_QD] = [];
+  this.data_[DNS_SECTION_AN] = [];
+  this.data_[DNS_SECTION_NS] = [];
+  this.data_[DNS_SECTION_AR] = [];
+};
+
+/**
+ * Parse a DNSPacket from an ArrayBuffer (or Uint8Array).
+ */
+DNSPacket.parse = function(buffer) {
+  let consumer = new DataConsumer(buffer);
+  if (consumer.short()) {
+    throw new Error('DNS packet must start with 00 00');
+  }
+  let flags = consumer.short();
+  let count = {};
+  count[DNS_SECTION_QD] = consumer.short();
+  count[DNS_SECTION_AN] = consumer.short();
+  count[DNS_SECTION_NS] = consumer.short();
+  count[DNS_SECTION_AR] = consumer.short();
+
+  let packet = new DNSPacket(flags);
+
+  // Parse the QUESTION section.
+  for (let i = 0; i < count[DNS_SECTION_QD]; ++i) {
+    let part = new DNSRecord(
+      consumer.name(),
+      consumer.short(),  // type
+      consumer.short()); // class
+    packet.push(DNS_SECTION_QD, part);
+  }
+
+  // Parse the ANSWER, AUTHORITY and ADDITIONAL sections.
+  [DNS_SECTION_AN, DNS_SECTION_NS, DNS_SECTION_AR].forEach(function(section) {
+    for (let i = 0; i < count[section]; ++i) {
+      let part = new DNSRecord(
+        consumer.name(),
+        consumer.short(),
+        consumer.short(), // class
+        consumer.long(),  // ttl
+        consumer.slice(consumer.short()));
+      packet.push(section, part);
+    }
+  });
+
+  if (consumer.isEOF()) {
+    DEBUG && debug('was not EOF on incoming packet');
+  }
+  return packet;
+};
+
+DNSPacket.prototype.push = function(section, record) {
+  this.data_[section].push(record);
+};
+
+DNSPacket.prototype.each = function(section) {
+  let filter = false;
+  let call;
+  if (arguments.length == 2) {
+    call = arguments[1];
+  } else {
+    filter = arguments[1];
+    call = arguments[2];
+  }
+  this.data_[section].forEach(function(rec) {
+    if (!filter || rec.type == filter) {
+      call(rec);
+    }
+  });
+};
+
+/**
+ * Serialize this DNSPacket into an ArrayBuffer for sending over UDP.
+ */
+DNSPacket.prototype.serialize = function() {
+  let out = new DataWriter();
+  let s = [DNS_SECTION_QD, DNS_SECTION_AN, DNS_SECTION_NS, DNS_SECTION_AR];
+
+  out.short(0).short(this.flags_);
+
+  s.forEach(function(section) {
+    out.short(this.data_[section].length);
+  }.bind(this));
+
+  s.forEach(function(section) {
+    this.data_[section].forEach(function(rec) {
+      out.name(rec.name).short(rec.type).short(rec.cl);
+
+      if (section != DNS_SECTION_QD) {
+        // TODO: implement .bytes()
+        throw new Error('can\'t yet serialize non-QD records');
+        //        out.long(rec.ttl).bytes(rec.data_);
+      }
+    });
+  }.bind(this));
+
+  return out.buffer;
+};
+
+/**
+ * DNSRecord is a record inside a DNS packet; e.g. a QUESTION, or an ANSWER,
+ * AUTHORITY, or ADDITIONAL record. Note that QUESTION records are special,
+ * and do not have ttl or data.
+ */
+let DNSRecord = function(name, type, cl, opt_ttl, opt_data) {
+  this.name = name;
+  this.type = type;
+  this.cl = cl;
+
+  this.isQD = (arguments.length == 3);
+  if (!this.isQD) {
+    this.ttl = opt_ttl;
+    this.data_ = opt_data;
+  }
+};
+
+DNSRecord.prototype.asName = function() {
+  return new DataConsumer(this.data_).name();
+};
+
+DNSRecord.prototype.asSRV = function() {
+  if (this.type !== DNS_REC_TYPE_SRV) {
+    return null;
+  }
+
+  let consumer = new DataConsumer(this.data_);
+  let data_length = this.data_.length;
+  return {
+    priority: consumer.short(),
+    weight: consumer.short(),
+    port: consumer.short(),
+    target: consumer.name() + consumer.name(),
+  };
+};
+
+DNSRecord.prototype.asTXT = function() {
+  if (this.type !== DNS_REC_TYPE_TXT) {
+    return null;
+  }
+
+  let consumer = new DataConsumer(this.data_);
+  let attributes = [];
+  while(!consumer.isEOF()) {
+    attributes.push(consumer.string());
+  }
+
+  return attributes;
+};
+
+/* end https://raw.githubusercontent.com/GoogleChrome/chrome-app-samples/master/mdns-browser/dns.js */
+
+/**
+ * Parse fully qualified domain name to service name, instance name,
+ * and domain name. See https://tools.ietf.org/html/rfc6763#section-7.
+ *
+ * example: The Server._http._tcp.example.com
+ *   instance name = "The Server"
+ *   service type = "_http._tcp"
+ *   domain = "example.com"
+ * @private
+ */
+function _parseDomainName(str) {
+  let items = str.split('.');
+  let idx = items.findIndex(function(element) {
+    return element === '_tcp' || element === '_udp';
+  });
+
+  return {
+    instanceName: items.splice(0, idx - 1).join('.'),
+    serviceType: items.splice(0, 2). join('.'),
+    domainName: items.join('.')
+  };
+}
+
+function _createPropertyBag(map) {
+  let bag = Cc['@mozilla.org/hash-property-bag;1']
+              .createInstance(Ci.nsIWritablePropertyBag);
+
+  for (let entry of map.entries()) {
+    bag.setProperty(entry[0], entry[1]);
+  }
+
+  return bag;
+}
+
+let MulticastDNS = function() {
+  this._targets = new Map();
+};
+
+MulticastDNS.prototype = {
+  socket: null,
+  //public API
+  startDiscovery: function(aServiceType, aListener) {
+    DEBUG && debug('startDiscovery for ' + aServiceType);
+    let { serviceType } = _parseDomainName(aServiceType);
+    this._addServiceListener(serviceType, aListener);
+
+    try {
+      this._ensureSocket();
+      this._query(serviceType + '.local', DNS_REC_TYPE_PTR);
+      aListener.onDiscoveryStarted(serviceType);
+    } catch (e) {
+      DEBUG && debug('onStartDiscoveryFailed: ' + serviceType + ' (' + e + ')');
+      this._removeServiceListener(serviceType, aListener);
+      aListener.onStartDiscoveryFailed(serviceType, Cr.NS_ERROR_FAILURE);
+    }
+  },
+
+  stopDiscovery: function(aServiceType, aListener) {
+    DEBUG && debug('stopDiscovery for ' + aServiceType);
+    let { serviceType } = _parseDomainName(aServiceType);
+    this._removeServiceListener(serviceType, aListener);
+
+    aListener.onDiscoveryStopped(serviceType);
+    if (this._targets.size === 0) {
+      DEBUG && debug('close current socket');
+      this.socket.close();
+      delete this.socket;
+    }
+  },
+
+  registerService: function(aServiceInfo, aListener) {
+    DEBUG && debug('service registration is not supported');
+    throw Cr.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  unregisterService: function(aServiceInfo, aListener) {
+    DEBUG && debug('service registration is not supported');
+    throw Cr.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  resolveService: function(aServiceInfo, aListener) {
+    DEBUG && debug('address info is already resolve during discovery phase');
+    aListener.onServiceResolved(aServiceInfo);
+  },
+
+  //private API
+  onReceive: function(info) {
+    let packet = DNSPacket.parse(info.rawData);
+    let serviceRecords = {};
+
+    packet.each(DNS_SECTION_AR, DNS_REC_TYPE_SRV, (rec) => {
+      DEBUG && debug('recieve SRV: ' + rec.name);
+      let srv = rec.asSRV();
+      serviceRecords[rec.name] = {
+        port: srv.port,
+        host: srv.target,
+      };
+    });
+
+    packet.each(DNS_SECTION_AR, DNS_REC_TYPE_TXT, (rec) => {
+      DEBUG && debug('recieve TXT: ' + rec.name);
+      if (!serviceRecords[rec.name]) {
+        return;
+      }
+
+      let txt =  rec.asTXT();
+      let attributes = new Map();
+      for(let x in txt) {
+        let idx = x.indexOf('=');
+        if (idx < 0) {
+          attributes.set(txt[x], true);
+          continue;
+        }
+
+        let key = txt[x].substring(0, idx);
+        let value = txt[x].substring(idx + 1);
+        attributes.set(key, value);
+      }
+      serviceRecords[rec.name].attributes = attributes;
+    });
+
+    packet.each(DNS_SECTION_AN, DNS_REC_TYPE_PTR, (rec) => {
+      DEBUG && debug('recieve PTR: ' + rec.name);
+      let { serviceType: answerType } = _parseDomainName(rec.name);
+      if (this._targets.has(answerType)) {
+        let name = rec.asName();
+        DEBUG && debug('>> for ' + name);
+        let {instanceName, serviceType, domainName} = _parseDomainName(name);
+        let serviceInfo = {
+          host: serviceRecords[name].host,
+          address: info.fromAddr.address,
+          port: serviceRecords[name].port,
+          serviceType: serviceType,
+          serviceName: instanceName,
+          domainName: domainName,
+          attributes: _createPropertyBag(serviceRecords[name].attributes),
+          QueryInterface: XPCOMUtils.generateQI([Ci.nsIDNSServiceInfo]),
+        };
+        this._targets.get(serviceType).forEach(function(listener) {
+          listener.onServiceFound(serviceInfo);
+        });
+      }
+    });
+  },
+
+  /**
+   * Handles network error occured while waiting for data.
+   * @private
+   */
+  onReceiveError: function(socket, status) {
+    DEBUG && debug('receiver socket error' + status);
+    return true;
+  },
+
+  /**
+   * Broadcasts for services on the given socket/address.
+   * @private
+   */
+  _query: function(search, type) {
+    DEBUG && debug('query for service: ' + search);
+    let packet = new DNSPacket();
+    packet.push(DNS_SECTION_QD, new DNSRecord(search, type, DNS_CLASS_IN | DNS_CLASS_QU));
+
+    this._broadcast(this.socket, packet);
+  },
+
+  /**
+   * Broadcasts a MDNS packet on the given socket/address.
+   * @private
+   */
+  _broadcast: function(sock, packet) {
+    let raw = new DataView(packet.serialize());
+    let length =  raw.byteLength;
+    let buf = [];
+    for (let x = 0; x < length; x++) {
+      let charcode = raw.getUint8(x);
+      buf[x] = charcode;
+    }
+    sock.send(MDNS_ADDRESS, MDNS_PORT, buf, buf.length);
+  },
+
+  _addServiceListener: function(serviceType, listener) {
+    let listeners = this._targets.get(serviceType);
+    if (!listeners) {
+      listeners = [];
+      this._targets.set(serviceType, listeners);
+    }
+
+    if (!listeners.find((element) => {
+          return element === listener;
+        })) {
+      DEBUG && debug('insert new listener');
+      listeners.push(listener);
+    }
+  },
+
+  _removeServiceListener: function(serviceType, listener) {
+    if (!this._targets.has(serviceType)) {
+      DEBUG && debug('listener doesnt exist');
+      return;
+    }
+
+    let listeners = this._targets.get(serviceType);
+    let idx = listeners.findIndex(function(element) {
+      return element === listener;
+    });
+
+    if (idx >= 0) {
+      listeners.splice(idx, 1);
+    }
+
+    if (listeners.length === 0) {
+      this._targets.delete(serviceType);
+    }
+  },
+
+  _ensureSocket: function() {
+    if (this.socket) {
+      DEBUG && debug('reuse current socket');
+      return;
+    }
+
+    this.socket = Cc['@mozilla.org/network/udp-socket;1']
+                    .createInstance(Ci.nsIUDPSocket);
+    let self = this;
+    this.socket.init(MDNS_PORT, false,
+                     Services.scriptSecurityManager.getSystemPrincipal());
+    this.socket.asyncListen({
+      onPacketReceived: function(aSocket, aMessage) {
+        self.onReceive(aMessage);
+      },
+
+      onStopListening: function(aSocket, aStatus) {
+        self.onReceiveError(aSocket, aStatus);
+      },
+    });
+    this.socket.joinMulticast(MDNS_ADDRESS);
+  },
+};

--- a/netwerk/dns/mdns/libmdns/moz.build
+++ b/netwerk/dns/mdns/libmdns/moz.build
@@ -5,16 +5,21 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
     EXTRA_COMPONENTS += [
         'nsDNSServiceDiscovery.js',
         'nsDNSServiceDiscovery.manifest',
     ]
 
+    EXTRA_JS_MODULES += [
+        'MulticastDNSAndroid.jsm',
+        'MulticastDNSFallback.jsm',
+    ]
+
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa' or \
         (CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gonk' and CONFIG['ANDROID_VERSION'] >= '16'):
     UNIFIED_SOURCES += [
         'MDNSResponderOperator.cpp',
         'MDNSResponderReply.cpp',
         'nsDNSServiceDiscovery.cpp',
     ]
 

--- a/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.js
+++ b/netwerk/dns/mdns/libmdns/nsDNSServiceDiscovery.js
@@ -1,18 +1,24 @@
 /* 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/. */
 "use strict";
 
 const { classes: Cc, interfaces: Ci, results: Cr, utils: Cu } = Components;
 
-Cu.import("resource://gre/modules/MulticastDNS.jsm");
+Cu.import('resource://gre/modules/Services.jsm');
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
+if (Services.prefs.getBoolPref("network.mdns.use_js_fallback")) {
+  Cu.import("resource://gre/modules/MulticastDNSFallback.jsm");
+} else {
+  Cu.import("resource://gre/modules/MulticastDNSAndroid.jsm");
+}
+
 const DNSSERVICEDISCOVERY_CID = Components.ID("{f9346d98-f27a-4e89-b744-493843416480}");
 const DNSSERVICEDISCOVERY_CONTRACT_ID = "@mozilla.org/toolkit/components/mdnsresponder/dns-sd;1";
 const DNSSERVICEINFO_CONTRACT_ID = "@mozilla.org/toolkit/components/mdnsresponder/dns-info;1";
 
 function log(aMsg) {
   dump("-*- nsDNSServiceDiscovery.js : " + aMsg + "\n");
 }
 
@@ -130,17 +136,17 @@ nsDNSServiceDiscovery.prototype = {
 
     return {
       QueryInterface: XPCOMUtils.generateQI([Ci.nsICancelable]),
       cancel: (function() {
         if (this.discoveryStarting || this.stopDiscovery) {
           this.stopDiscovery = true;
           return;
         }
-        this.mdns.stopDiscovery(aServiceType, this);
+        this.mdns.stopDiscovery(aServiceType, listener);
       }).bind(listener)
     };
   },
 
   registerService: function(aServiceInfo, aListener) {
     log("registerService");
     let listener = new ListenerWrapper(aListener, this.mdns);
     listener.registrationStarting = true;
@@ -148,17 +154,17 @@ nsDNSServiceDiscovery.prototype = {
 
     return {
       QueryInterface: XPCOMUtils.generateQI([Ci.nsICancelable]),
       cancel: (function() {
         if (this.registrationStarting || this.stopRegistration) {
           this.stopRegistration = true;
           return;
         }
-        this.mdns.unregisterService(aServiceInfo, this);
+        this.mdns.unregisterService(aServiceInfo, listener);
       }).bind(listener)
     };
   },
 
   resolveService: function(aServiceInfo, aListener) {
     log("resolveService");
     this.mdns.resolveService(aServiceInfo, new ListenerWrapper(aListener));
   }