Firefox – Use Google Data Compression Proxy

Using the Google Chrome Data Compression Proxy on non-Chrome browsers involves two steps.

1. Set your HTTP proxy to proxy.googlezip.net and port 80.
2. For each of your requests, calculate and inject a Chrome-Proxy header into your request.

The Chrome-Proxy header should contain the following string: ps=<timestamp>-<num1>-<num2>-<num3>, sid=<md5 string>, b=<build>, p=<patch>, c=<platform> where:

• timestamp: is the current number of seconds elapsed since unix epoch
• num1, num2, num3: are random numbers which can be set to 0
• md5 string: is the md5 of the auth string
• auth string: "<timestamp>" + "<auth key>" + "<timestamp>"
• auth key: ac4500dd3b7579186c1b0620614fdb1f7d61f944
• build: Chrome build number, can be set to 2214
• patch: Chrome patch number, can be set to 115
• platform: Chrome platform, can be set to "win"

As an full example of the header you might have: Chrome-Proxy: ps=1439961190-0-0-0, sid=9fb96126616582c4be88ab7fe26ef593, b=2214, p=115, c=win

Now, to implement this practically, I think the easiest solution is to use an extension but there does not appear to be one for firefox that already has this functionality.

Therefore, I have implemented my own firefox extension for Firefox version 38 or above that allows anyone to use the Google Chrome Data Compression Proxy on firefox and am including the code below.

The following is the procedure that I used to develop and test the extension, and would allow others to regenerate the extension from scratch.

1. Get and install nodejs

2. Use npm from nodejs to install jpm via npm install jpm

   Note that some versions of Ubuntu package node as nodejs so if jpm can't find node you may need to install another distribution of nodejs or create a link for node to nodejs

3. Create a new directory for the extension and cd into it

4. jpm init

5. Answer prompts with defaults

6. Replace your index.js with the code provided below

7. jpm run

   Note that if jpm is unable to find firefox in the standard locations, you'll also need to pass the -b flag to jpm to tell it where to find your browser. (e.g. jpm run -b /path/to/Firefox/Nightly)

You should now have firefox open with this new extension loaded and all traffic proxied through the Google Chrome Data Compression Proxy during this session.

Because jpm run creates a temporary profile, you will need to jpm run this extension anytime you'd like your traffic proxied. You could also jpm xpi and Install Add-on From File in Add-On manager.

You can verify that your data is being proxied by examining the response headers for the Via header which indicates data being sent over the Chrome Compression Proxy (e.g. Via: "1.1 Chrome-Compression-Proxy")

You can determine how much data you are saving by comparing the Content-Length header to the X-Original-Content-Length header in server responses.

Code for index.js follows:

/*
 * Data Compressor Proxy 0.0.1
 * License: MPL
 *
 * Based on
 * Data Compression Proxy Extension for Google Chrome on Desktop
 * (c) 2014 Jerzy Glowacki. License: Apache 2.0

 * and includes
 * JavaScript MD5 1.0.1
 * https://github.com/blueimp/JavaScript-MD5
 * Copyright 2011, Sebastian Tschan
 * https://blueimp.net
 * Licensed under the MIT license:
 * http://www.opensource.org/licenses/MIT
 *
 * JavaScript MD5 1.0.1 is Based on
 * A JavaScript implementation of the RSA Data Security, Inc. MD5 Message
 * Digest Algorithm, as defined in RFC 1321.
 * Version 2.2 Copyright (C) Paul Johnston 1999 - 2009
 * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
 * Distributed under the BSD License
 * See http://pajhome.org.uk/crypt/md5 for more info.
 */

var self = require('sdk/self');
var { Class } = require('sdk/core/heritage');
var { Unknown } = require('sdk/platform/xpcom');
var {Cc, Ci} = require("chrome");
var prefsvc = require("sdk/preferences/service");

var httpRequestObserver = Class(
{
  extends:  Unknown,
  interfaces: [ 'nsIObserver' ],
  topic: '*',
  observe: function(subject, topic, data)
  {
    if (topic == "http-on-modify-request") {
      var httpChannel = subject.QueryInterface(Ci.nsIHttpChannel);
      httpChannel.setRequestHeader("Chrome-Proxy", this.authHeader(), false);
    }
  },

  get observerService() {
    return Cc["@mozilla.org/observer-service;1"]
                     .getService(Ci.nsIObserverService);
  },

  authHeader : function() {
    var authValue = 'ac4500dd3b7579186c1b0620614fdb1f7d61f944';
    var timestamp = Date.now().toString().substring(0, 10);
    return 'ps=' + timestamp + '-' + '0' + '-' + '0' + '-' + '0' + ', sid=' + md5(timestamp + authValue + timestamp) + ', b=2214' + ', p=115' + ', c=win';
  },

  register: function()
  {
    this.observerService.addObserver(this, "http-on-modify-request", false);
  },

  unregister: function()
  {
    this.observerService.removeObserver(this, "http-on-modify-request");
  }
});

var httprequestobserver = httpRequestObserver();
httprequestobserver.register();
prefsvc.set("network.proxy.http", "proxy.googlezip.net");
prefsvc.set("network.proxy.http_port", 80);
prefsvc.set("network.proxy.type", 1);

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